Input of various kinds of information to an image processing device by use of a foot part of a user is enabled in order not to cause a difference between an image that changes and a feeling with respect to the motion of the body of the user. Position indicators are disposed at a sole back part of a foot-part position indicating instrument. A foot-part position detecting device receives a position indication signal from the position indicators, detects whether the foot-part position indicating instrument makes forward movement that is movement in the extension direction of a line extended in a direction from a heel-side part toward a toe-side part or makes backward movement that is movement in the extension direction of a line extended in a direction from the toe-side part toward the heel-side part, and indicates the forward movement and the backward movement to the image processing device.