Before game data is arranged, a storage area for the game data in an internal memory is determined so that each game parameter is stored in a different storage area each time the game data is arranged. Then, arrangement information that directly or indirectly indicates the storage area for each game parameter is stored in a specified area of the internal memory. Then, the game data is loaded from an external storage medium to the determined storage area. Moreover, when a game parameter in the internal memory needs to be referred to or overwritten during the game process, the storage area for the game parameter is determined by referring to the arrangement information. Thus, it is possible to prevent general users from easily modifying the game data.