PURPOSE: To enable the pressure to be transformed without specially requiring a driving energy for producing a high pressure by a method wherein a reciprocating movement similar to that on a primary side is transferred to a secondary side, and secondary high pressure circuit is formed by a suction-discharge valve unit on the secondary side.
CONSTITUTION: Pressure oil is flowed in a piston rear chamber A of a low pressure cylinder 1 through a passage Q from a change-over valve chamber G and thrusts a piston rod 8. At this time, waste oil in a front chamber B is discharged to passages S, W, change-over valve chambers N, M and an oil discharge port T, so that the piston rod 8 advances. Further, at the same time, a pressure of the waste oil in a piston front chamber D of a high pressure cylinder 2 is increased to block the suction valve 22, while the pressure oil push-opens the discharge valve 23, flows into a piston rear chamber C and a part thereof is discharged as a high pressure oil from a high pressure discharge port 24. Therefore, the pressure can be transformed without requiring the special driving energy.