PURPOSE: To enable the breaking of wire of a lamp to be detected by a very few elements by driving through only one power switch a plurality of lamps connected in parallel, and comparing a load current value flowing through the lamps with a reference value to detect breaking of a lamp.

CONSTITUTION: The lamps 1W4 connected in parallel are driven by the single power switch 5. Let the power source voltage be VCC, and the load current be I0, then the magnitude of the load current I0 can be detected as a voltage VRO between the ends of a load current detecting resistor R0, and is compared at a voltage comparator 6 with a reference value Vref. If all of the four lamps are in normal condition, the following relation can be established: VRO>Vref, and if the wire of one or more lamps are broken, the following relation can be established: VRO<Vref. In the case of VRO<Vref, a lamp-broken signal S0 is outputted through a gate circuit 7. The reference value Vref is a voltage generated by resistors R1, R2, R3 and a diode D1, the power source voltage VCC is impressed to one end of the resistor R2, and a fixed voltage VDD is impressed to one end of the resistor R3.