A first game controller that can be used by both a first game apparatus and a second game apparatus transmits its operation data by using a data format having a first data region including a header, a second data region including key data, and a third data region including data of an extended controller. A second game controller that can be used by the first game apparatus also uses a data format having similar three data regions, but the second data region is merely secured as a region, while all operation information is included in the third data region and transmitted.