PURPOSE: To prevent malfunction or action instability for a high frequency oscillation circuit and an intermediate amplifier circuit.

CONSTITUTION: A coil 2 for excitation is disposed close to an electrodeless discharge lamp 1. High frequency power is supplied to the excitation 2 from a high frequency circuit block 9 comprising a high frequency oscillation circuit 3, an intermediate amplifier circuit, and a power amplifier circuit 5 of larger power consumption in this order, and DC power is supplied to the high frequency circuit block 9 from a DC power supply circuit 7. Mounted wire lengths between a feed point 7c of the DC power supply circuit 7 and feed points of the intermediate amplifier circuit 4 and the power amplifier circuit 5 are set in such a way that the power amplifier circuit 5 becomes the shortest, and that the intermediate amplifier circuit 4 and the high frequency oscillation circuit 3 are longer in this order. Return of an induction current to the intermediate amplifier circuit 4 and the high frequency generation circuit 3 through a floatation capacity can be restricted, and malfunction and action instability of the high frequency oscillation circuit 3 and the intermediate amplifier circuit 5 can be prevented.