PURPOSE: To operate a device with a good power factor in the whole operating frequency area, by connecting the element of the most improved power factor according to the area of operating frequency.

CONSTITUTION: By a frequency controlling circuit 14, the operating frequency (f) of an inverter 12 is controlled. By a comparing circuit 15, the frequency (f) and a set value (f1) are compared with each other, and when f≥f1, then a switch S1 is turned ON, and when f<f1, then a switch S2 is turned ON. By the ON/OFF-control of the switches S1, S2, according to the area of the operating frequency (f), power factor improving reactors L1 and L2 are switched. Accordingly, a power factor for the operating frequency (f) is to be kept to be of a high value in the whole area of the operating frequency (f).