A pair of gripping sections performs opening and closing operations along a base member through displacement of a piston by means of a pressure fluid supplied to a chuck body. A pair of fingers, which constitute the gripping sections, is openable and closable in directions perpendicular to opening/closing directions of the gripping sections, by means of a driving force supplied from a driving section. The gripping sections are positioned with respect to a workpiece by actuating the pair of fingers to perform the opening/closing operation. Thereafter, by supplying the pressure fluid, the workpiece is gripped at a desired gripping position by means of the gripping sections.