A stage apparatus includes an X-direction movable member provided parallel to a reference plane and relatively movable thereto only in a specific X-direction via an X-direction guide device; a Y-direction movable member supported by the X-direction movable member thereon to be movable only in a Y-direction orthogonal to the X-direction of the reference plane via a Y-direction guide device, wherein the X-direction movable member is provided in between a stationary support plate, which is parallel with the reference plane, and the Y-direction movable member; three ball retaining through-holes formed in the X-direction movable member at three vertices of an imaginary triangle; and three balls installed in respective the three ball retaining through-holes so as to contact the stationary support plate and the Y-direction movable member, wherein the three ball retaining through-holes allow each of the three balls to rotate in any rotational direction therein.