To provide a game system that enables a degree of difficulty of an occurrence of a predetermined game event to be changed depending on a degree of proficiency of a player in a game in which the predetermined event is made to occur when a controller is operated according to specific procedures. The present invention relates to a game system including one or more controllers. In the game system, a determining unit (52) determines whether or not a criterion operation data string has been inputted from the controller, a game event generation unit (58) generates a predetermined game event according to a result of the determination made by the determining unit (52), and the determining unit (52) changes the criterion operation data string based on a result of a past determination on at least one of the one or more controllers.