Objectives The COVID-19 pandemic spread rapidly across the globe during the first half of 2020. In Japan, a state of emergency was declared on April 7, 2020, which had a significant impact on the life of citizens. This study focused on behaviors like avoiding going out or coming in contact with others and frequent hand-washing to prevent the infection and the spread of COVID-19 among people living in Tokyo. We also examined the factors associated with these behaviors during the declaration of emergency.Methods An online survey was conducted from April 26 to 29, 2020, approximately 20 days after the declaration of the emergency, among men and women aged 20-69 years living in Tokyo. The study framework was based on the protection motivation theory, which explains the risk-reducing behaviors, and focus theory of normative conduct, which explains the effect of others' behavior on one's own behavior. The frequency of behaviors like avoiding going out or coming in contact with others and frequent hand-washing, as well as the perception of the risk of COVID-19 during the week preceding the survey, were assessed. Each preventive action was evaluated based on the following factors: perceived effectiveness (response efficacy), perceived practicability (self-efficacy), necessary cost (response cost), and perceptions of how much should be done (injunctive norm) and how well others are doing it (descriptive norm). Hierarchical multiple regression analysis with these behaviors as outcomes were performed.Results This study included 1,034 participants (50.3% male, mean age 44.82 years, standard deviation 14.00 years). The analyses of the frequency of avoiding going out or coming in contact with others showed that the injunctive norm was positively associated with the behavior (standardized partial regression coefficient (β)=0.343, P<0.001), while the descriptive norm was negatively associated with the behavior (β=-0.074, P=0.010). Furthermore, the two-way interaction between risk perception, response efficacy, and self-efficacy was significant (β=0.129, P<0.001), indicating that risk perception was positively associated with the behavior only when either response efficacy or self-efficacy was low. A similar analysis conducted for hand-washing behavior revealed that injunctive norm (β=0.256, P<0.001) and response efficacy (β=0.132, P<0.001) were positively associated with the behavior, while the response cost (β=-0.193, P<0.001) was negatively associated with the behavior.Conclusion Some variables in the protection motivation theory and the focus theory of normative conduct were related to the behavior for the prevention of COVID-19. The results suggest that the application of these theories is useful in future studies.