PURPOSE: To facilitate the control of a pump by providing a condenser for compensating the phase of a lag current flowing into the pump against the phase of applying voltage and constructing the title device in such a way as to control the source voltage applied to a parallel connected body of the pump and the condenser, and a transistor.

CONSTITUTION: A phase advancing condenser 2 is parallely connected to a pump 1 with its one end connected to an alterating electric power terminal T1, and the phase of a lag current flowing into the pump 1 is made compensable against the phase of voltage applied to the pump 1. A diode bridge 3 formed of four diodes D1-D4 is also provided, and the one alterating current input terminal IA1 is connected to the connected point between the pump 1 and the condenser 2 as well as the other alterating current input terminal IA1 is connected to an alterating electric power terminal T2. In addition, a NPN type transistor 4 is provided having its collector connected to the positive output terminal OP of a steam bridge 3 and its emitter to the negative output terminal OM respectively, and this transistor 4 is controlled by a transistor control circuit 5.