PURPOSE:To obtain an ample pressing force with a comparatively low hydraulic pressure without using a hydraulic cylinder by expanding two thrust members through a wedge abutting on the outer peripheral surface of a rubber expanded by hydraulic pressure. CONSTITUTION:In a pressing operation, an object to be pressed is inserted between an active plate 2 and a passive plate 3 and hydraulic pressure is supplied uniformly from a hydraulic pressure generating device to the rubber tube 6 through a manifold 9 and a hydraulic pipe 8. The rubber tube 6 having a closed top end is expanded by this hydraulic pressure and pushes the wedge 7 in contact with the tube sides forward. As a result, each wedge 7 bites between the thrust members 5 in the shape of a wedge and expands the thrust members 5. Since in one of these thrust members 5 its displacement is regulated by a base 10, the other thrust member 5 is pushed up as a result and the object is pressed between the active plate 2 supported by this thrust member 5 and the passive plate 3.