To prevent a pump from being overloaded.

A discharge side relief valve 130 is installed parallel with a discharge valve 102 between a discharge member 100 and a pump chamber 84. When a liquid pressure in the pump chamber 84 is increased according to the forward movement of a piston 80, the discharge valve 102 is opened, and hydraulic fluid in the pump chamber 84 is discharged to the discharge chamber 100. When the fluid pressure in the pump chamber 84 is lowered according to the backward movement of a piston 80, the discharge valve 102 is closed. When the liquid pressure in the discharge chamber 100 is excessively high, a difference between the liquid pressure in the discharge chamber 100 and the liquid pressure in the pump chamber 84 is more than a relief pressure and the discharge side relief valve 130 is opened. The hydraulic fluid in the discharge chamber 100 is allowed to flow into the pump chamber 84, and the liquid pressure in the discharge chamber 100 is lowered. Thus, the liquid pressure in the discharge chamber 100 is prevented from being excessively increased, and the pump is prevented from being overloaded.