PURPOSE: To heat a pump by applying two coils to the coil part of an electric motor for driving the pump and connecting the two coils in parallel during pump operation and in series during pump stop, respectively to power supplies.

CONSTITUTION: A pump device has switches 5 to 7 connected to the (a) side and power supplies 8a and 8b feed electric power, with main coils 2a and 2b and auxiliary coils 3a and 3b connecting in parallel. When an electric motor 1 is stopped, the switches 5 to 7 are connected to the other side, and the power supply 8a is connected to the other power supply 8b via the electric motor 1 connecting sequentially the auxiliary coils 3b and 3a and the main coils 2a and 2b in series. According to the aforesaid constitution, heat generation is available from the coils during the rest of the pump and the freezing thereof can be prevented.