PURPOSE: To cope with discharge lamps within a wide range by use of one kind with a simple circuit structure by detecting the input current of an inverter circuit, and comparing the detected quantity of electricity with a preset threshold to detect the state of a high pressure discharge lamp.

CONSTITUTION: The voltage of a resistor R0 proportional to a detected input current is transformed by a transformer T1, rectified by a diode bridge, and charged in a capacitor C4 through a resistor R10. The voltage of the capacitor C4 is thus proportional to the input current, and until it reaches the Zener voltage of a Zener diode ZD3, a transistor Q13 is in the opened state. A TRIAC Q11 is laid in the opened state to light an incandescent lamp IL. When the Zener voltage of the diode ZD3 is set to the capacitor C4 corresponding to a threshold, the incandescent lamp IL is lighted for a determined period. Since the state of a high pressure discharge lamp can be detected by the magnitude relation between the preset threshold and the detected input quantity of electricity, thus, discharge lamps within a wide range can be coped with by use of one kind with a simple circuit.