A direct-current converter includes a high-frequency converting circuit converting voltage of a direct-current power source to alternating-current voltage, a transformer having primary and secondary windings P, S and a rectification smoothing circuit rectifying and smoothing voltage induced in the secondary winding. This converting circuit includes other transformer having first and second windings n1, n2, switching element Q1 having a source connected to a negative pole of the power source and a drain connected to a positive pole thereof through winding n1, and switching element Q2 having a source connected to the negative pole of the power source and a drain connected to the positive pole thereof through winding n2, element Q2 being turned on/off alternately to element Q1 being turned on/off. Winding P is connected to a point between winding n1 and the drain of element Q1 and another point between winding n2 and the drain of element Q2.