<p>With the purpose of evaluating the transmission risk of novel coronavirus 2019 (COVID-19) and the effectiveness of countermeasures at school graduation and entrance ceremonies, this study examined various event conditions during an assumed ceremony attended by 865 participants, including singing, diploma conferment, and ceremonial address, and built an infection risk evaluation model that takes into account the effectiveness of countermeasures such as mask wearing during the ceremony. With the conditions assumed in this study, the average risk of infection per asymptomatic infected person attending a graduation ceremony was 4.0×10^-5 (0.035 for a graduation ceremony attended by 865 people) when no preventive measures such as wearing a mask were taken. The average risk of infection per asymptomatically infected person attending an entrance ceremony with the same conditions mentioned above was 1.2×10^-5 (0.010 for an entrance ceremony attended by 865 people) when no measures were taken, suggesting that the average risk of infection was higher at graduation ceremonies. In the graduation ceremony, the risk of infection when measures were taken to wear masks only during singing was 2.2×10^-5 (0.019 for a graduation ceremony attended by 865 people), and the average risk of infection among participants was reduced by about 45% when non-woven masks were worn during singing. Although the risk of infection at graduation and entrance ceremonies is low even without any countermeasures, a combination of various countermeasures will be effective if the infection rate in the community increases.</p>