PURPOSE: To prevent the occurence of arc, etc., by constituting the high voltage coil of a flyback transformer by thermosoftening wires and interrupting power supply when the voltage of the high voltage winding is higher than first reference voltage or lower than second reference voltage.

CONSTITUTION: When discharge is generated due to the open-circuit or short circuit of the high voltage coil 8 of a flyback transformer 4, higher voltage generates in the coil 8 than usual. The voltage of the point A of the transformer 4 is detected at a resistance R1, a diode D1 of a protective circuit 9. A comparator Cn 1 outputs L when the voltage is higher than a reference voltage Eref 1, it is inverted in an inverter In and H is imparted to an OR circuit 10. When the transformer 4 is discharged or ignites due to the discharge of a horizontal circuit and it is heated up to around 150°C, the coil 8 fuses because it is constituted by thermosoftening wires. A comparator Cn2 outputs H when detected voltage is lower than a reference voltage Eref 2 and it is inputted in the OR circuit 10. As a result, a power supply interruption circuit 11 interrupts a power supply line which is not shown by a figure by the output of the OR circuit 10.