To hasten build-up of luminous flux to prevent a breakdown of a dimming relay.

A main choke L1 as a ballast, a dimming choke L2, and a starter built-in high-pressure discharge lamp 2 are provided through a commercial power source V1 and a self-holding switch SW1. Here, a normally closed contact Ry-b of a relay Ry is connected in parallel to the choke L2. A self- holding hand switch SW2, the relay Ry and a switch SW3 are connected in series on the power source side of the choke L2. A transformer 5 as a lighting detecting means is connected to a power source line a of the power source V1 and the discharge lamp 2 such that the line a passes through the transformer 5. The secondary side of the transformer 5 is connected with the input side of a rectifier 6, further with the input side of a control circuit 7. The circuit 7 is provided with a timer, to start clocking when the output of the rectifier 6 is input into the circuit 7. When the clocking gets to the prescribed time, the circuit 7 controls the switch SW3 from an open state to a closed state.