PURPOSE: To obtain an effective absorption amount to the stroke of a displacement lever by making a diaphragm operate a linear movement by the synergism of a leaf spring which has a double-spring structure, when a linear displacement is given to the driving member of the diaphragm.

CONSTITUTION: A diaphragm 2, a leaf spring 3, and a displacement lever 7 are provided on a pump main body 1, and the rotation around the rotary shaft 4 of a motor is converted into a linear reciprocating movement of the displacement lever 7 by an eccentric axis center 5 so as to give a linear movement to the diaphragm 2. Since the leaf spring 3 has a double-spring structure to exercise a synergism, an effective absorption amount to the stroke of the displacement lever 7 is obtained.