A forward direction line is set on a course, in a virtual game world, on which a player object is allowed to move. An advancing direction at a current position of the player object is determined based on the forward direction line. The advancing direction is determined as a direction in which the player object advances so as to control a movement of a player character in accordance with an acceleration instruction, and a leftward-rightward movement instruction from a player. Consequently, it is possible to assist the player in controlling a direction in which an object operated by the player moves.