Interest in pet robots and virtual pets is currently increasing along with the pet boom. Pet robots and virtual pets have been found to be therapeutic. However, what characteristics of pet robots and virtual pets are therapeutically effective have yet to be clarified. In this study, we carried out experiments to compare the therapeutic effects between pet robots and virtual pets in terms of physical embodiment from psychological and physiological aspects. Psychological evaluation results showed that the reduction in the tension score and increase in the vigor score with pet robots were significantly higher than those with virtual pets. Physiological evaluation results showed that the increase in the percentage of alpha waves with pet robots was significantly higher than that with virtual pets. These results suggest that physical interaction is an element for reducing mental strain and improving vitality.