A direct-current converter that includes: a first series circuit, which is connected in parallel with a smoothing capacitor and in which a first switching element and a second switching element are connected in series; a second series circuit, which is connected in parallel between main electrodes of the first switching element and in which a resonance capacitor, a resonance reactor and a primary winding of a transformer are connected in series; a half wave rectification smoothing circuit, which rectifies and smoothes a voltage of a secondary winding of the transformer; a control circuit configured to alternately turn on and off the first switching element and second switching element, based on an output voltage of the rectification smoothing circuit; and a third series circuit, which is connected in parallel with the second switching element and in which a boost reactor and a direct-current power supply are connected in series.