A superfinishing stone (2) is slid on a rotating subject surface (7) as pressed against the subject surface (7) and is held in contact against the subject surface (7) as vibrated thereon in a different direction from the sliding direction. The superfinishing stone includes a plurality of stone portions (3, 4) divided by a split surface (6) inclined to both the sliding direction and the vibrating direction and mutually independently movable along the split surface (6) and in the pressing direction.