People are exposed to various stimuli every day, and they receive various levels of stress strengths from them. Stress influences working of the autonomic nervous system. It has been reported that long-term stress may be an illness trigger. In this research, the change in working of the autonomic nervous mental system was measured under several kind of workloads and during physical exercise, and working of the parasympathetic nervous system (which is an index of relaxation level) was guessed from the heart beat rate and the LF/HF value of the change at the R-R intervals. As a result, taking a stroll in nature, reading a favorite book and listening to classical music were recommended as suitable ways to obtain relaxation.