PURPOSE: To previously heat a discharge tube by a control with the simple structure at a low cost without using a heater for maintaining temperature of a discharge tube and a temperature control circuit, and to obtain the excellent light emitting luminance under the stabilized discharge condition at the time of lighting.

CONSTITUTION: A display plate is provided in the front surface of a case, and a discharge unit for using a discharge tube 1 housed in the case and plural incandescent lamp 3 provided near the discharge tube 1 to transmit the light through the display plate for lighting is provided. A control unit 7 for switching the lighting condition between the discharge tube 1 and the incandescent lamp 3 in response to the open degree of a choke valve of an auto-choke mechanism 6 provided in a vehicle side is provided.