PURPOSE: To prevent pulsating delivery of pump while to simplify the structure by providing a chamber and a relief valve while coupling each other at the pump head section having plural reciprocal members the delivery phase of which is shifted each other.

CONSTITUTION: The reciprocal pump is constituted into a double pump where a pump 48 forming a plunger pump section 1 is juxtaposed with another pump 48 having 180° phase shifted eccentric driving cam. Here, a chamber 22 and a relief valve 28 are arranged while coupled each other at the pump head section 21. The chamber 22 is arranged in front of the head housing 5 while communicating to the outside of a check valve 37 in a delivery path 36 of respective plunger pump 1 through a communication path 39. While the relief valve 28 has the inlet 41 communicated through a communication path 40 to the chamber 22 and the outlet 42 communicated through a communication path 43 to the outside of a check valve 38 in suction path 35 of respective plunger pump section 1.