When reaching a cracking pressure, the check valve will be pushed open, resulting in running oil only in one direction. The check valve is pushed down by pilot pressure from the outside, resulting in being possible to change the flow in a reverse direction. It is incorporated in a circuit requiring prevention of descent due to dead load of oil hydraulic cylinder.

Furthermore, a piston type accumulator has been incorporated in the cylinder circuit, resulting in being possible to maintain oil pressure for a long time.