PURPOSE: To provide a mixture light lighting system, which can prevent breakdown and failure of a HID lamp and a stabilizer when the BID lamp is fitted wrong and which encourages a user to correct the connection and of which circuit structure is simplified.

CONSTITUTION: A voltage detecting circuit 12 for detecting voltage of a BID lamp and an abnormality detecting circuit 12 for detecting connection-error of the HID lamp on the basis of the abnormality of lamp voltage to open a switch 2 are provided in a lighting circuit, which includes a stabilizer 10 for lighting a HID lamp having a larger rated lamp voltage. Breakdown of the HID lamp 11 during the lighting under the overload condition is thereby avoided, and a user is encouraged to reset the connection of the lighting circuit and the HID lamp 11 to the normal connection. Since the connection error of the HID lamp is detected by comparing the lamp voltage value with a reference voltage, structure of the circuit is simplified. The switch 2 is not turned on till it is manually reset after it is opened once to prevent the repetition of lighting and delighting and to prevent the shortening of lifetime of the stabilizer 10 and the HID lamp 11.