To prevent the occurrence of ununiform brightness during use of argon tubes lighted with DC.
A commercial AC power is converted into a high frequency power by a high frequency inverter 12, and the voltage is boosted by a transformer 13, and the secondary output is rectified by a diode 27 or 28 and supplied to argon tubes 15 for lighting. When a breaker 35 is switched ON, the AND of an electricity recovery detection output B and a using state detection output D drives a stepping relay 55 to change over a switch 29, which reverses the polarities of the DC power supplied to the argon tubes 15. The electricity recovery detection output B is delayed and supplied to the gates 45, 46, and the switch 29 is changed over before the inverter starts operating. The AND of the inverted output I of the output D and the output B does not change over the switch 29 for an ON-OFF control. The switch 29 is changed over for every time when the breaker 35 is turned ON.