A game apparatus includes a hand-held housing, a display screen, and a gyro sensor for detecting an angular velocity of a rotation around an axis perpendicular to the display screen. When the player rotates the game apparatus around the axis, a rotation angle of the housing is calculated based on the detected angular velocity. The display screen displays a game image including a rotational image rotated according to the rotation angle and an irrotational image controlled independently of the rotation angle. The rotational image is controlled so as to rotate in a direction opposite to the rotation angle and by the same degree of angle as the rotation angle, for example. It thus appears to the player that the rotational image stands still and the irrotational image makes a rotational movement. The progress of the game is changed according to a result of the determination.