To enhance responsiveness to stroke changeover, reduce a radial size for compactness and relax accuracy need in working parts.

A pressure intensifier 3 and a control valve mechanism 4 are provided inside a main case 2, a changeover of an oil passage is carried out by the control valve mechanism 4 thereby successively actuating the pressure intensifier 3, and a primary pressure supplied from a primary port 6 is intensified by the pressure intensifier 3 to be discharged into a secondary port 8. The pressure intensifier 3 and the control valve mechanism 4 are serially arranged, and a movement of a piston 10a is directly transmitted to the control valve mechanism 4 via a spool 41.