To facilitate handling and reduce noise.

An inner cylinder 1 and an outer cylinder 2 which are arranged coaxially are held between a head cover 4 and a rod cover 6, and a ring shaped piston 12 is slidably inserted between the inner cylinder 1 and the outer cylinder 2. A plurality of piston rods 18 are erected on a piston 12 so as to form a cylinder 25. A motor 28 and a hydraulic pump 30 which is driven by the motor 28 are housed in the inner cylinder 1, and also a hydraulic tank according to the volume of the piston rod 18 is housed so as to close both ends of the inner cylinder 1. A hydraulic circuit for driving a cylinder 25 is formed in the inner cylinder 1.