diff --git a/TIASshot/Utils/IoUtil.cs b/TIASshot/Utils/IoUtil.cs
index 3bbd776..95f9d16 100644
--- a/TIASshot/Utils/IoUtil.cs
+++ b/TIASshot/Utils/IoUtil.cs
@@ -29,7 +29,9 @@
                         var valStrs = line.Split(',');
                         if (cols == -1) cols = valStrs.Length;
                         else if (cols != valStrs.Length) throw new Exception("cols != valStrs.Length");
-                        var vals = valStrs.Select(x => double.Parse(x)).ToArray();
+                        // CSV はピリオド小数で記述される仕様のため，OS ロケールに依存せず解釈する
+                        var vals = valStrs.Select(
+                            x => double.Parse(x, System.Globalization.CultureInfo.InvariantCulture)).ToArray();
                         arr.Add(vals);
                     }
                 }
@@ -56,7 +58,9 @@
                     var line = "";
                     for (var col = 0; col < m.Cols; col++) {
                         if (col > 0) line += ",";
-                        line += $"{m.At<double>(row, col):0.0000000}";
+                        // カンマ小数ロケールでは小数点が列区切りと衝突するため，常にピリオド小数で出力する
+                        line += m.At<double>(row, col).ToString(
+                            "0.0000000", System.Globalization.CultureInfo.InvariantCulture);
                     }
                     writer.WriteLine(line);
                 }