In a mahjong game system constituted by a mahjong game machine and an information processing device, the information processing device comprises: game data reception means for receiving game data; game data storage means; ranking criterion setting means for setting a ranking criterion during the creation of a ranking list at predetermined time intervals based on the game data; ranking means for creating, on the basis of the ranking criterion, a ranking list based on the stored game data; and ranking data transmitting means for transmitting the ranked ranking data to the mahjong game machine.