diff --git a/CMakeLists.txt b/CMakeLists.txt
index 24e400c..5f62c14 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -34,7 +34,7 @@ endif()
 
 set(CMAKE_CXX_STANDARD 11)
 if (MSVC)
-  set(CMAKE_CXX_FLAGS "/O2 /W4 /wd4244 /wd4305 /wd4996 /EHsc")
+  set(CMAKE_CXX_FLAGS "/O2 /W4 /wd4100 /EHsc")
 else()
   set(CMAKE_CXX_FLAGS "-O2 -Wall -Wno-deprecated-register")
 endif()
diff --git a/include/SPTK/utils/int24_t.h b/include/SPTK/utils/int24_t.h
index 81cbbe7..af0f99c 100644
--- a/include/SPTK/utils/int24_t.h
+++ b/include/SPTK/utils/int24_t.h
@@ -29,8 +29,9 @@ class int24_t {
   int24_t() {
   }
 
-  explicit int24_t(int initial_value) {
-    *this = initial_value;
+  template <typename T>
+  explicit int24_t(T initial_value) {
+    *this = static_cast<int>(initial_value);
   }
 
   ~int24_t() {
diff --git a/include/SPTK/utils/uint24_t.h b/include/SPTK/utils/uint24_t.h
index 2415131..c69d4ff 100644
--- a/include/SPTK/utils/uint24_t.h
+++ b/include/SPTK/utils/uint24_t.h
@@ -28,8 +28,9 @@ class uint24_t {
   uint24_t() {
   }
 
-  explicit uint24_t(int initial_value) {
-    *this = initial_value;
+  template <typename T> 
+  explicit uint24_t(T initial_value) {
+    *this = static_cast<int>(initial_value);
   }
 
   ~uint24_t() {
diff --git a/src/analysis/pitch_extraction_by_reaper.cc b/src/analysis/pitch_extraction_by_reaper.cc
index 32c9076..baff048 100644
--- a/src/analysis/pitch_extraction_by_reaper.cc
+++ b/src/analysis/pitch_extraction_by_reaper.cc
@@ -16,7 +16,7 @@
 
 #include "SPTK/analysis/pitch_extraction_by_reaper.h"
 
-#include <algorithm>  // std::copy, std::fill
+#include <algorithm>  // std::copy, std::fill, std::transform
 #include <cmath>      // std::ceil
 #include <cstdint>    // int16_t
 
@@ -54,7 +54,9 @@ bool PitchExtractionByReaper::Get(
 
   reaper::EpochTracker epoch_tracker;
   epoch_tracker.set_unvoiced_cost(static_cast<float>(voicing_threshold_));
-  std::vector<int16_t> integer_waveform(waveform.begin(), waveform.end());
+  std::vector<int16_t> integer_waveform(waveform.size());
+  std::transform(waveform.begin(), waveform.end(), integer_waveform.begin(),
+                 [](double x) { return static_cast<int16_t>(x); });
   if (!epoch_tracker.Init(integer_waveform.data(),
                           static_cast<int32_t>(integer_waveform.size()),
                           static_cast<float>(sampling_rate_),
diff --git a/src/analysis/spectrum_extraction_by_world.cc b/src/analysis/spectrum_extraction_by_world.cc
index 537296e..b5016d1 100644
--- a/src/analysis/spectrum_extraction_by_world.cc
+++ b/src/analysis/spectrum_extraction_by_world.cc
@@ -62,7 +62,7 @@ bool SpectrumExtractionByWorld::Run(
       f0_floor = f0[i];
     }
   }
-  if (f0_floor < world::GetF0FloorForCheapTrick(sampling_rate_, fft_length_)) {
+  if (f0_floor < world::GetF0FloorForCheapTrick(static_cast<int>(sampling_rate_), fft_length_)) {
     return false;
   }
 
@@ -73,7 +73,7 @@ bool SpectrumExtractionByWorld::Run(
   }
 
   world::CheapTrickOption option;
-  world::InitializeCheapTrickOption(sampling_rate_, &option);
+  world::InitializeCheapTrickOption(static_cast<int>(sampling_rate_), &option);
   option.fft_size = fft_length_;
   option.f0_floor = f0_floor;
 
diff --git a/src/conversion/autocorrelation_to_composite_sinusoidal_modeling.cc b/src/conversion/autocorrelation_to_composite_sinusoidal_modeling.cc
index d2db611..a1408fb 100644
--- a/src/conversion/autocorrelation_to_composite_sinusoidal_modeling.cc
+++ b/src/conversion/autocorrelation_to_composite_sinusoidal_modeling.cc
@@ -117,7 +117,7 @@ bool AutocorrelationToCompositeSinusoidalModeling::Run(
         const int index((l < 2 * k) ? (2 * k - l) : (l - 2 * k));
         sum += (binomial_coefficient)*input[index];
       }
-      u[l] = sum / std::pow(2.0, l);
+      u[l] = static_cast<double>(sum / std::pow(2.0, l));
     }
 
     for (int i(0); i < num_sine_wave_; ++i) {
diff --git a/src/main/acr2csm.cc b/src/main/acr2csm.cc
index 6eba95e..13a3667 100644
--- a/src/main/acr2csm.cc
+++ b/src/main/acr2csm.cc
@@ -81,7 +81,7 @@ int main(int argc, char* argv[]) {
   double convergence_threshold(kDefaultConvergenceThreshold);
 
   for (;;) {
-    const char option_char(getopt_long(argc, argv, "m:i:d:h", NULL, NULL));
+    const int option_char(getopt_long(argc, argv, "m:i:d:h", NULL, NULL));
     if (-1 == option_char) break;
 
     switch (option_char) {
diff --git a/src/main/bcp.cc b/src/main/bcp.cc
index 6417283..dfdf6fe 100644
--- a/src/main/bcp.cc
+++ b/src/main/bcp.cc
@@ -87,13 +87,13 @@ class BlockCopy : public BlockCopyInterface {
  public:
   BlockCopy(int input_start_number, int input_end_number,
             int input_block_length, int output_start_number,
-            int output_block_length, T pad_value, bool is_ascii = false)
+            int output_block_length, double pad_value, bool is_ascii = false)
       : input_start_number_(input_start_number),
         input_end_number_(input_end_number),
         input_block_length_(input_block_length),
         output_start_number_(output_start_number),
         output_block_length_(output_block_length),
-        pad_value_(pad_value),
+        pad_value_(static_cast<T>(pad_value)),
         is_ascii_(is_ascii) {
   }
 
@@ -125,7 +125,7 @@ class BlockCopy : public BlockCopyInterface {
           }
           if (input_start_number_ <= i && i <= input_end_number_) {
             try {
-              inputs[i] = std::stold(word);
+              inputs[i] = static_cast<T>(std::stold(word));
             } catch (std::invalid_argument&) {
               return false;
             }
diff --git a/src/main/c2acr.cc b/src/main/c2acr.cc
index c633c70..385b3d5 100644
--- a/src/main/c2acr.cc
+++ b/src/main/c2acr.cc
@@ -85,7 +85,7 @@ int main(int argc, char* argv[]) {
   int fft_length(kDefaultFftLength);
 
   for (;;) {
-    const char option_char(getopt_long(argc, argv, "m:M:l:h", NULL, NULL));
+    const int option_char(getopt_long(argc, argv, "m:M:l:h", NULL, NULL));
     if (-1 == option_char) break;
 
     switch (option_char) {
diff --git a/src/main/csm2acr.cc b/src/main/csm2acr.cc
index b966a81..77b0d53 100644
--- a/src/main/csm2acr.cc
+++ b/src/main/csm2acr.cc
@@ -80,7 +80,7 @@ int main(int argc, char* argv[]) {
   int num_order(kDefaultNumOrder);
 
   for (;;) {
-    const char option_char(getopt_long(argc, argv, "m:h", NULL, NULL));
+    const int option_char(getopt_long(argc, argv, "m:h", NULL, NULL));
     if (-1 == option_char) break;
 
     switch (option_char) {
diff --git a/src/main/pitch_mark.cc b/src/main/pitch_mark.cc
index c0e8358..c1e7014 100644
--- a/src/main/pitch_mark.cc
+++ b/src/main/pitch_mark.cc
@@ -294,7 +294,7 @@ int main(int argc, char* argv[]) {
 
   switch (output_format) {
     case kBinarySequence: {
-      int next_pitch_mark(pitch_mark.empty() ? -1 : std::round(pitch_mark[0]));
+      int next_pitch_mark(pitch_mark.empty() ? -1 : static_cast<int>(std::round(pitch_mark[0])));
       for (int i(0), j(1); i < waveform_length; ++i) {
         if (i == next_pitch_mark) {
           if (!sptk::WriteStream(binary_polarity, &std::cout)) {
@@ -304,7 +304,7 @@ int main(int argc, char* argv[]) {
             return 1;
           }
           if (j < num_pitch_marks) {
-            next_pitch_mark = std::round(pitch_mark[j++]);
+            next_pitch_mark = static_cast<int>(std::round(pitch_mark[j++]));
           }
         } else {
           if (!sptk::WriteStream(0.0, &std::cout)) {
@@ -334,7 +334,7 @@ int main(int argc, char* argv[]) {
       const double bias(kSine == output_format ? 0.0 : 0.5 * sptk::kPi);
       for (int n(0), i(0); n <= num_pitch_marks; ++n) {
         const int next_pitch_mark(
-            n < num_pitch_marks ? std::round(pitch_mark[n]) : waveform_length);
+            n < num_pitch_marks ? static_cast<int>(std::round(pitch_mark[n])) : waveform_length);
         // Find the point across voiced region to unvoiced one.
         int j(i);
         for (; j < next_pitch_mark; ++j) {
diff --git a/src/main/x2x.cc b/src/main/x2x.cc
index b268b81..d26eef4 100644
--- a/src/main/x2x.cc
+++ b/src/main/x2x.cc
@@ -122,7 +122,7 @@ class DataTransform : public DataTransformInterface {
         *input_stream >> word;
         if (word.empty()) break;
         try {
-          input_data = std::stold(word);
+          input_data = static_cast<T1>(std::stold(word));
         } catch (std::invalid_argument&) {
           return false;
         }
@@ -133,7 +133,7 @@ class DataTransform : public DataTransformInterface {
       }
 
       // Convert.
-      T2 output_data(input_data);
+      T2 output_data(static_cast<T2>(input_data));
 
       bool is_clipped(false);
       {
diff --git a/src/utils/sptk_utils.cc b/src/utils/sptk_utils.cc
index f0bb06b..d45bbbc 100644
--- a/src/utils/sptk_utils.cc
+++ b/src/utils/sptk_utils.cc
@@ -136,7 +136,7 @@ bool ReadStream(bool zero_padding, int stream_skip, int read_point,
       return false;  // Something wrong!
     }
 
-    std::fill_n(sequence_to_read->begin() + end - num_zeros, num_zeros, 0.0);
+    std::fill_n(sequence_to_read->begin() + end - num_zeros, num_zeros, static_cast<T>(0));
 
     return !input_stream->bad();
   }
@@ -336,7 +336,9 @@ bool ConvertSpecialStringToDouble(const std::string& input, double* output) {
 
   std::string lowercase_input(input);
   std::transform(input.begin(), input.end(), lowercase_input.begin(),
-                 [](unsigned char c) { return std::tolower(c); });
+                 [](unsigned char c) {
+                   return static_cast<unsigned char>(std::tolower(c));
+                 });
   if ("pi" == lowercase_input) {
     *output = sptk::kPi;
     return true;