The first coronavirus 2019 (COVID-19) patients were reported in China on December 12, 2019, and the first COVID-19 patients were reported in Japan on January 16, 2020. Here, we investigated the number of patients in Emergency Departments (EDs) in three major hospitals in Tokyo, and also briefly discussed about the relationship between the number of patients in EDs and health system's capacity. We compared the number of patients in 2020 to the average number of patients from 2016 to 2019. Numbers were compared in three periods: before the first COVID-19 patient was reported in Japan (January 1 to January 16), after the government encouraged social distancing (February 26 to March 10), and the interval between them (January 17 to February 25). The average number of daily patients in 2020 ( = 122) decreased by 17% compared to the average number of patients from 2016 to 2019 ( = 144) (Mann-Whitney test,  < 0.001). This phenomenon might be due to a fear of contracting the virus at hospitals, companies having their employees work remotely and postponing events, people following the Japanese Ministry of Health, Labour and Welfare's instructional guidelines for going to the hospital, prevention awareness becoming widespread, and a decreased number of tourists. The number of patients visiting Emergency Departments in Tokyo was decreased and the number of COVID-19 infections has remained within the health system's capacity during the early phase of COVID-19 first wave.