A power factor correcting current resonance converter comprising: a current resonance converter circuit; and a power factor correcting converter circuit cascade-connected in a previous stage of the current resonance converter circuit; wherein switching operation of the power factor correcting converter circuit is performed in synchronization with switching operation of the current resonance converter circuit; wherein the current resonance converter circuit includes: a first switch and a second switch connected in series to each other; a resonance capacitor (Cr); a resonance inductor (Lr); a transformer having a first winding provided on a primary side and a second winding, a voltage being produced in the second winding in response to turn-on/turn-off of the first switch and the second switch, and a winding on a secondary side connected to a rectifying/smoothing circuit; and a control circuit (CONT) turning on or off the first switch based on the voltage produced in the second winding; wherein a series circuit consisting of the resonance capacitor (Cr), the resonance inductor (Lr), and the first winding is connected in parallel to the first switch or the second switch; wherein the power factor correcting converter circuit includes a choke coil (Lp) having one end receiving a voltage provided by rectifying a commercial alternating-current input power source, a diode connected to the other end of the choke coil (Lp) or to a tap provided in a winding of the choke coil (Lp), and a third switch; and wherein the third switch is turned on or off in response to the voltage produced in the second winding of the transformer; characterized in that: the power factor correcting converter circuit further includes a smoothing capacitor (Cs) smoothing a current passing through the diode; wherein the third switch connects a connection point of the choke coil (Lp) and the diode to a low potential side of the smoothing capacitor (Cs). a current resonance converter circuit; and a power factor correcting converter circuit cascade-connected in a previous stage of the current resonance converter circuit; wherein switching operation of the power factor correcting converter circuit is performed in synchronization with switching operation of the current resonance converter circuit; wherein the current resonance converter circuit includes: a first switch and a second switch connected in series to each other; a resonance capacitor (Cr); a resonance inductor (Lr); a transformer having a first winding provided on a primary side and a second winding, a voltage being produced in the second winding in response to turn-on/turn-off of the first switch and the second switch, and a winding on a secondary side connected to a rectifying/smoothing circuit; and a control circuit (CONT) turning on or off the first switch based on the voltage produced in the second winding; a first switch and a second switch connected in series to each other; a resonance capacitor (Cr); a resonance inductor (Lr); a transformer having a first winding provided on a primary side and a second winding, a voltage being produced in the second winding in response to turn-on/turn-off of the first switch and the second switch, and a winding on a secondary side connected to a rectifying/smoothing circuit; and a control circuit (CONT) turning on or off the first switch based on the voltage produced in the second winding; wherein a series circuit consisting of the resonance capacitor (Cr), the resonance inductor (Lr), and the first winding is connected in parallel to the first switch or the second switch; wherein the power factor correcting converter circuit includes a choke coil (Lp) having one end receiving a voltage provided by rectifying a commercial alternating-current input power source, a diode connected to the other end of the choke coil (Lp) or to a tap provided in a winding of the choke coil (Lp), and a third switch; and wherein the third switch is turned on or off in response to the voltage produced in the second winding of the transformer; the power factor correcting converter circuit further includes a smoothing capacitor (Cs) smoothing a current passing through the diode; wherein the third switch connects a connection point of the choke coil (Lp) and the diode to a low potential side of the smoothing capacitor (Cs).