The alert regarding the emergence of novel influenza was issued by the WHO on April 24th, and the government has taken immediate actions to respond to the situation since then. Based on the presumption that a pandemic was imminent, countermeasures for the H1N1 influenza pandemic have been prepared by establishing and implementing effective public health crisis strategies over the past few years. Our main strategy during the pandemic influenza crisis has shifted in accord with the corresponding National Disaster Phases. In the Caution (Containment) Phase, our main goal was to contain the influx of disease from overseas. We focused on measures such as entry screening and quarantine inspection while monitoring travelers arriving from affected countries. In the Alert Phase I, our aim was deceleration and prevention of secondary community outbreaks through enhanced early detection. We intensified our surveillance and response system for possible mass outbreaks. During Alert Phase II, as the influenza had spread widely, our tactics switched to minimizing social and economic impact and preventing severe cases with early administration of antiviral agents, especially among high-risk patients. In the current Severe Phase, we are trying to reduce mortality cases with intensive care. Since we have implemented mass vaccination, we predict an early termination of the pandemic.