To easy perform the adjustment of a neutral position and the inclining operation of a movable swash plate by performing the fine adjustment of the neutral position and the movement of a spool valve by an adjustment link when the swash plate of the variable delivery hydraulic pump is inclined and controlled by a hydraulic servo mechanism.

A hydraulic servo mechanism 61 mounted on a variable delivery hydraulic pump for inclining and controlling a swash plate, stores a servo piston 71 in a cylinder chamber 70a, and a pin shaft 190 projecting from a side portion of a movable swash plate is fitted to a side face of the servo piston 71. A spool valve 72 is fitted into an axial through hole of the servo piston 71, and a pin 159 fixed to one end of an adjustment link is fitted into an engagement groove 161 formed on a lower outer periphery of the spool valve 72. The position of the pin 159 is adjustable by an eccentric shaft, the adjustment link is displaced through a solenoid on the basis of the overload information of an engine, whereby the inclination of the swash plate is controlled.