Abstract: A reciprocating pump, in which a pressure control valve has a pressure-receiving face and is supported to a valve seat bearing at least one of suction and discharge valves, the pressure-receiving face being disposed within a discharge passage, and at a cylinder head is provided a pressure adjuster for a control spring biasing the pressure control valve to the valve seat, so that the pressure control valve, which functions as a relief valve, safety valve or unloader valve, may be incorporated with a main body of the pump so as to simplify construction and decrease the number of parts, thereby making the pump less expensive to produce, smaller in size, and lighter in weight.