PURPOSE: To permit the easy dealing with the change of pump capacity, etc. by freely switching the control constant of a constant-pressure control means for controlling the electricity supply amount to a pump motor according to the output pressure of the pump, in an electrical pump which uses a common pump for a plurality of loads.

CONSTITUTION: The pressure and the flow rate of the water in a water feeding pipe 6 connected to a pump 2 driven by a motor 3 are detected by a pressure detecting means 13 and a flow-rate detecting means 14, respectively, and the outputs of the detecting means 13 and 14 are input into a controller 25. Said controller 25 allows an electricity supply starting means 16 to output an electricity supply starting signal when the water feeding pressure lowers below a prescribed value, and a constant- pressure control means 17 controls an electricity supply control means 15 so that the water supply pressure is made nearly constant by controlling the electricity supply amount to the motor 3 according to the variation of the water supply pressure. The control constant (control value) of the constant-pressure control means 17 can be switched by a control-value determining means 61 through the switching operation of a control-valve switching means 60, and easy dealing with the change of pump capacity, etc. is permitted.