Objectives: The aim of this study was to elucidate the physiological adjustment effect of forest therapy based on the Law of Initial Value. Methods: The experiments were conducted in nine forest and urban areas in Japan during the period from 2011 to 2012. There were 12 male Japanese university students participating in each of the nine experiments (total, 108 participants). Of these, 98 subjects (mean age ± standard deviation, 21.4 ± 1.6 years) were analyzed. The subjects were instructed to view a real forest landscape or urban area for 15 min. The systolic blood pressure, diastolic blood pressure, and pulse rate of each subject were measured. We analyzed the correlation between the initial values (after city viewing) and the differences in values between the two environments (after forest viewing–after city viewing). Results: There was a negative correlation between the initial values and the differences in values between the two environments. The subjects whose initial systolic blood pressure, diastolic blood pressure, and pulse rate were high showed marked decreases in these parameters as their response after viewing the forest environment, whereas those whose initial systolic blood pressure, diastolic blood pressure, and pulse rate were low showed increases in these parameters as their response. Conclusions: These results support the premise that the physiological effect of a forest environment can differ depending on a subject’s initial response values. Moreover, it was clear that forest therapy caused physiological adjustment, normalizing blood pressure and pulse rate.