To provide a diaphragm pump for expanding a flow rate controllable range to a maximum flow rate of a pump while controlling a very small flow rate.

This diaphragm pump has an installation base 1 incorporated with an electric motor and a pump head 2 incorporated with a valve mechanism; and is constituted so as to suck fluid in a pump chamber 4 via a vent hole 6 from a suction chamber 5 and deliver the fluid to a delivery chamber 8 via a vent hole 7 from the pump chamber 4 by operating a suction valve 10 and a delivery valve 13 by reciprocatably operating a diaphragm 3 by an eccentric cam fixed to a rotary shaft of the electric motor; and is constituted so that the suction valve 10 or the delivery valve 13 opening-closing the vent hole 6 arranged in a partition wall 9 formed on the pump head, operates even when a rotating speed of the electric motor reduces and a reciprocating motion of the diaphragm 3 is slow, and the suction valve 10 or the delivery valve 13 are installed on the partition wall 9 of the pump head 2 for adjusting the very small flow rate of 10% or less of the maximum flow rate.