The aim of this study was to investigate the change of Heart Rate Variability(HRV) that mild cold stimulus on the forehead of healthy men induces. 34 healthy male subjects participated in the experiments. On the first test series, 15 subjects were applied to the mild cold stimulus by the devise for cold stimulation. In the second test series, 10 subjects With heat Syndrome and 5 subjects With cold Syndrome were applied to the mild cold Stimulus. Aa a additional test, 4 subjects with cold syndrome were applied to the warm stimulus in the last test series. We analyzed the HRV through measuring electrocardiogram.(ECG). The result of this study is comparatively clear. In the first test series, mild cold stimulus made parasympathetic nervous system be activated. In the second test series, mild cold stimulus made parasympathetic nervous system be activated both in subjects with heat syndrome and subjects with cold syndrome, and heat syndrome shows more active parasympathetic nervous system rather than cold syndrome subjects do. In the last test series, 2 subjects with cold syndrome respond the mild cold stimulus. That means warm stimulus of cold condition subjects made parasympathetic nervous system active in 2 of 4 subjects. We found out that mild cold stimulus on forehead makes parasympathetic nervous system be activated in healthy male, and it can be interpreted that mild cold stimulus make healthy human be relaxed. Also, subjects have different fondness of thermal stimulus according to their Cold or Heat condition Preferences. Last test series shows that we need to investigate effect of the warm stimulus heat syndrome subjects.