A power factor is improved using a simplified structure without particularly providing a power factor improving circuit, and high efficiency is obtained. For this purpose, one terminal of a direct-current power source 12, from which a pulsating current is obtained, is connected through a choke coil 13 to one end of an auxiliary coil 14c constituting a converter transformer 14; the other end of the auxiliary coil 14c is connected to the other terminal of the direct-current power source 12 through a series circuit of a diode 15 and a capacitor 16; a connection midpoint between the diode 15 and the capacitor 16 is connected to one end of a primary coil 14a of the converter transformer 14; the other end of the primary coil 14a is connected to the other terminal of the direct-current power source 12 through a switching element 17; a secondary coil 14b of the converter transformer 14 is connected to direct-current voltage output terminals 19a and 19b through a rectifying circuit 18; the direct-current voltage output terminal 19a is connected to an input side of a pulse width modulation control circuit 20; and an output terminal of the pulse width modulation control circuit 20 is connected to a control electrode of the switching element 17.