Plane position coordinates indicating a position of a player object in a plane game field is updated based on an action which is performed by the player object on the plane game field and is determined according to an input signal. The plane position coordinates in a coordinate system based on the plane game field are converted into coordinates in a coordinate system based on a game field of a curved surface, thereby obtaining curved surface position coordinates. Based on the curved surface position coordinates, the player object is positioned in the game field of the curved surface and displayed on a display screen.