To provide a power supply circuit that does not require a direction of the battery so that an accident such as a trouble or failure, leakage of liquid, or burst of the equipment may not happen when the direction of the battery is wrong.

In the circuit, a CMOS transistor is arranged for each electrode of a battery and thereby, the direction of the current flowing in the equipment is made constant by the selection effect of the CMOS transistor, in whichever direction the current flows according to the direction of the battery, and this circuit is built in the equipment.