Subacute thyroiditis (SAT) is a disorder of the thyroid gland and difficult to diagnose. It is probably triggered by a viral infection. Recently, several articles have reported SAT after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, reports describing SAT after SARS-CoV-2 in Japan are lacking. We herein report the first case of SAT after SARS-CoV-2 infection in Japan. After SARS-CoV-2 infection, some patients can develop not only pneumonia but also SAT. Thus, a careful follow-up is recommended for patients after SARS-CoV-2 infection. Furthermore, the effect of SARS-CoV-2 infection on thyroid dysfunction should not be ignored.