A game system for reliably realizing synchronization of timings at which a common event in a plurality of game machines start. The game system includes a plan management server that measures lapse of system time common in the game system and with the time measurement, updates plan information indicative of remaining time until the system time reaches a process start stage at which a process for the common event starts. Each of the game machines includes an obtaining device to obtain the plan information from the plan management server, a stage determining device to determine whether the system time has reached the process start stage or not on the basis of laps of time of the system time measured in the game machine, and a process executing device to start a process for the common event when it is determined that the system time has reached the process start stage.