PURPOSE: To smoothly start an inverter device by adding a softly starting function to an inverter circuit, and suppressing the abnormal voltage rise of a chopper circuit to gradually raise the voltage as a time elapses.

CONSTITUTION: An inverter device which supplies power to a load lamp lcompreses one switching element (Tr) Q1 of an inverter circuit C used also as an input power factor improving chopper B. The inverter circuit C comprises a series circuit of Trs Q1, Q2 which are alternately turned ON and OFF, and a half bridge circuit of diodes D1, D2 and capacitors C5, C6 connected in parallel with the series circuit, and is controlled to be driven by a switching control circuit SC. The ON duty of both the TRs Q1, Q2 are gradually varied at the time of starting to increase the Tr Q1 from 0% and to decrease the Tr Q2 from100%. As a result, it can prevent a smoothing condenser C2 from abnormally rising at its voltage at the time of starting to smoothly start it.