PURPOSE: To improve the pumping efficiency with precise actions of suction and exhaust valves, by using a diaphragm driving cam that can extend its staying time at the bottom and top death points of the diaphragm.

CONSTITUTION: The vertical movement of a diaphragm 4 compresses or expands a pumping chamber 8 and feed or exhaust a medium through a suction valve 5 and exhaust valve 6. A diaphragm driving cam 9 having a sliding surface 10 that can extend its staying time at the top and bottom death points of the diaphragm 4 is fitted to a cam shaft 11, and the sliding face 10 is brought together with the diaphragm 4. The shape of the cam 9 appropriate for this purpose is, for example, an arc cam having an arc face from A to D (about 90 degrees) with a radius of the shortest distance (forming the top death point) from the cam shaft center and an arc face from B to C with a radius of the longest distance (forming the bottom death point of the diaphragm 4).