PURPOSE: To provide an electromagnetic shield body, reduce radiation noises, and prevent or reduce the deterioration of the starting property of a discharge lamp by the electromagnetic shield body.

CONSTITUTION: An electromagnetic shield body 4 is provided near a high- frequency-lighted discharge lamp 2 connectably to the common potential to the ground potential of a high-frequency generator 1, and a switch device 5 disconnecting the electromagnetic shield body 4 from the ground potential at the time of the start of the discharge lamp 2 and connecting it during lighting is provided. The switch device 5 disconnects the electromagnetic shield body 4 from the ground potential, the high-frequency current from the high-frequency generator 1 is hardly leaked to the ground, the lamp current apt to become unstable at the time of the start is secured, and the deterioration of the starting property of the discharge lamp 2 can be prevented or reduced. After the discharge lamp 2 is lighted, the switch device 5 connects the electromagnetic shield body 4 to the ground potential, and the electromagnetic shield body 4 can effectively serve to reduce radiation noises.