To reduce operation noise and vibration by fitting an eccentric cam plate to a screw rotary shaft rotated by means of a motor, and connecting the extreme end part of a ring plate fitted in the link hole of the root end part with the eccentric cam plate to a rod expanding/contracting the bellows of a diaphragm pump.

A pump device 1 for a water tank is set on the water tank T, and a motor 2 is driven in this state so as to rotate rotary shafts 2A, 2B. By this rotation, an eccentric cam plate fitted in the link hole provided on the root end part through an intermediate ring and fitted to the rotary shaft 2A is rotated so as to reciprocate a ring plate 4 in the horizontal direction, the bellows made of rubber of a diaphragm pump 5 is repeated to expand and contract, and compressed air is forcedly fed from an accumulator 6 to a foam generator 8 through an air feed hose 7, so as to generate fine foam in service water W. In addition, the screw 2S in a pump chamber 11 is rotated by the rotary shaft 2B, the sevice water W is taken through an intake port 13, fed to a filter vessel 16, and circulated into the water tank again after filtering.