When there is an instruction for rotation during a game in a first field, a CPU core of a game apparatus obtains central coordinates in a second field after the rotation and coordinates (central coordinates) of a player object and BG object in steps S53 and S55. Then, the CPU core executes a rotation process in a hardware calculation circuit, for example, in steps S57 to S61. When detecting end of the rotation in a step S63, the CPU core executes a map switch process in a step S65. In the map switch process, the CPU core generates a second field according to second area data. Then, after generating the second field, the CPU core makes a hit determination according to the second area data in a step S7, for example.