To solve the problem wherein existing auxiliary power circuits have a voltage dropper for effecting a stable operation even if an input voltage varies, and loss in the voltage dropper reduces efficiency and generates heat.

An auxiliary power circuit includes: voltage conversion means 31 for converting an AC voltage to output a first AC voltage VA and a second AC voltage VB lower than the first AC voltage VA; first and second rectification means 32, 33 for rectifying the first and second AC voltages VA, VB to output first and second auxiliary winding voltages Va, Vb; voltage detection means 34 for outputting an undervoltage detection signal S34 when the second auxiliary winding voltage Vb is equal to or lower than a threshold voltage; and output voltage supply means 35 for outputting the first auxiliary winding voltage Va when the undervoltage detection signal S34 is input, and outputting the second auxiliary winding voltage Vb except when the undervoltage detection signal S34 is not input. This can dispense with a voltage dropper in the auxiliary power circuit to avoid efficiency reduction and heat generation attributable to loss in the voltage dropper.