To prevent a pulsing phenomenon of discharged fluid by providing a first base body in which a diaphragm is disposed and has a first discharge port and a suction port and a second base body in which a cavity communicating with the first discharge port is formed and is combined with the side wall of the first base body and has a second discharge port.

Fluid is filled in space (A) between an arc-like partition plate 23 and a body 22 of an air chamber 20 and lower space (B) inside the partition plate 23 and air is filled in upper space (C) inside the partition plate 23. A check ball 15 of a discharge side is released during a discharge stroke when a diaphragm 110 is moved forward to discharge fluid flowing into a pump room 130 during a previous suction stroke into the air chamber 20 through a communicating hole 16, which increases the pressure of the fluid in the air chamber 20 to compress the air in the space (C). That is, all the fluid flowing into the air chamber 24 is not discharged through a discharge pipe 24 but part of the fluid is introduced inside the partition plate 23, which prevents a rapid change in the discharge flow rate.