PURPOSE: To expand the range of pump operation and relax on the starting frequency even when the capacity of the pressure tank is small by linking the fitting part of a pressure switch to a pressure reducing unit.

CONSTITUTION: Jet unit 26 is provided between pump 10 and tank 12, and pressure switch is linked to jet unit 26. Hence, when a flow of water above a certain quantity passes the jet unit, by the jet action the pressure in the pressure reducing chamber drops, and pressure switch 14 is maintained ON even if the discharge pressure is higher than the OFF pressure of the pressure switch. When water is not used with faucet 24 closed, water is stored in pressure tank 12, but the pressure reducing action of jet unit 26 is gradually lowered, the pressure in pressure reducing unit 32 rises, the pressure switch is turned off and the pump stops. Since the operation range of the pump is expanded, it is not necessary to raise the operation frequency even if the capacity of the pressure tank is reduced.