Provided is a transformer having resonant inductance, the transformer including a core that includes a first leg formed in one side thereof, a second leg which is formed in the other side thereof so as to be electromagnetically coupled to the first leg, and a third leg which is formed between the first and second legs so as to be electromagnetically coupled to the first and second legs; a primary winding that is wound around one side of the third leg; a secondary winding that is wound around the other side of the third leg so as to induce power through electromagnetic induction with the primary winding; and a resonant inductance winding that is wound around the outside of the core so as not to be magnetically induced by magnetic fluxes generated from the primary and secondary windings.