A pneumatic chamber 20 is configured to include a first pneumatic chamber 21 pressurizing a first piston 11 and a second pneumatic chamber 22 pressurizing a second piston 12. The first pneumatic chamber 21 and the second pneumatic chamber 22 communicate with each other through a communication hole 87 formed via the inside of a retaining bolt 17. The second pneumatic chamber 22 is formed in a hydraulic pressure generating unit 55 moving in a thrust direction in a cylinder 2 and is separable from the first pneumatic chamber 21. In addition, the communication hole 87 is also separated into a communication hole 87a and a communication hole 87b with the corresponding separation, a rod portion 50 of the first piston 11 is also separated into a rod portion 50a and a rod portion 50b, and the communication hole 87b and the rod portion 50b are formed to be movable along with the hydraulic pressure generating unit 55 in the thrust direction.