PURPOSE: To obtain reduction in starting torque stably over a long period of time by arranging a communicating part to communicate a pump chamber with an external part.

CONSTITUTION: An air pump is provided with an eccentric driving shaft 13 arranged on an output shaft of a motor 1, an operation rod 4 to make reciprocating motion in the diameter direction of the motor by rotation of the driving shaft 13 and plural diaphragms 3 which are formed in a three-dimensional cubic shape and are driven by the reciprocating motion of the operation rod, and is also provided with a fine cross-sectional areal communicating part 6 in which the diaphragms 3 constitute a wall surface and which is composed of pump chambers 5 communicated with the external part through an intake valve 51 and an exhaust valve 52 and communicates the pump chambers 5 always with the external part.