There is provided a power supply circuit, in which cost reduction is realized by reducing the number of electric wires. An inverter 3 and a motor 4 are supplied with power by a high-voltage battery 21. Relays 22a to 22c are provided between the high-voltage battery 21 and the inverter 3. Both ends of each of relay coils C provided to the relays 22a to 22c are connected to an ECU 5, and the ECU 5 controls a current flowing through the relay coils C and thereby controls the turning on and off of the relays 22a to 22c. A service plug 6 is detachably provided between batteries making up the high-voltage battery 21, and when the service plug 6 is detached, the supply of power from the high-voltage battery 21 to the inverter 3 and the motor 4 is blocked and when the service plug 6 is attached, the supply of power from the high-voltage battery 21 to the inverter 3 and the motor 4 is enabled. An interlock switch 7 is turned off when the service plug 6 is detached, is turned on when the service plug 6 is attached, and is connected between the ECU 5 and the relay coils C.