To generate large thrust by a servomotor of low torque by comprising a control cylinder connected to a driving cylinder, and the servomotor for driving the control cylinder.

A driving cylinder 1 and a control cylinder 3 are hydraulically connected, and the operation of the control cylinder 3 is transmitted to the driving cylinder 1. A moving amount of the driving cylinder is represented by a formula (1), and the driving cylinder moves by LD when the control cylinder 3 moves by LC. The thrust is represented by a formula (2), and the driving cylinder generates the thrust FD when the thrust FC is added to the control cylinder 3. Accordingly the thrust, speed and position of the driving cylinder 1 can be controlled by controlling and operating the control cylinder 3. LD=LC (SC/SD)...(1) in which LD is a moving amount of the driving cylinder, LC is a moving amount of the control cylinder, SD is a sectional area of the driving cylinder part, SC is a sectional area of the control cylinder part. FD=FC(SD/ SC)...(2) in which FD is thrust of the driving cylinder, and FC is thrust of the control cylinder.