A game apparatus stores input positions detected by the input device at predetermined time intervals, in order of detection, into a memory of the game apparatus. Next, a trail vector indicating at least a portion of a trail drawn by the player on the input surface is calculated from the input positions. Further, a reference vector whose starting point is a predetermined position on the input surface and whose ending point is a position determined by the trail vector is calculated. An action of a player's character is determined based on an angle between the trail vector and the reference vector.