A servo regulator includes a servo piston coupled with a swash plate, a pressure chamber provided to face an end portion of the servo piston, a spool configured to control a pressure in the pressure chamber by being moved by a solenoid, a biasing member configured to bias the spool against a thrust of the solenoid, and a feedback portion configured to change a biasing force of the biasing member in accordance with tilting of the swash plate, wherein the feedback portion is coupled with the swash plate via the servo piston.

The present invention relates to a system preventing the pressured oil leakage in a cylinder line enabling very low leakage rates without using the valve or the system, or without reducing the diametrical space between the housing and spool.