PURPOSE: To detect power failure surely and to turn off a keep relay rapidly by connecting a control logical circuit discriminating the ON and OFF status of a power supply switch and generating a control signal for the keep relay.

CONSTITUTION: The control logical circuit 5 monitors the power supply switch periodically, and since potential B is not zero when the power supply switch 9 is in the off status, discrimintes the off status of the switch 9 and interrupts the generation of a control signal D. If power failure is restored and input voltage A is supplied after interrupting the input voltage A when the power failure is generated and a switch 6b of the keep relay 6 is in the on status, the control logical circuit 5 discriminates the on or off status of the power supply switch 9 and generates a control signal D to turn off the keep relay 6. Thus, incorrect control due to the recovery of the power failure can be prevented by operating the power supply switch 9 to turn on the power supply and operating a VTR.