To achieve the reduction in size of a pulse transformer simultaneously with reduction of leak inductance, and also to achieve the prevention of breakdown thereof simultaneously with the reduction of leak inductance.

The pulse transformer includes a magnetic core, and primary winding and secondary winding composed of low-voltage electric wires concentrically wound on the magnetic core. The primary winding and the secondary winding are uniformly and closely wound, and the wound primary winding and secondary winding are molded by silicon potting. Since the field intensity in a space part between the windings can be kept high by the molding of the primary winding and the secondary winding by the silicon potting, dielectric breakdown between the windings can be prevented. Further, since the coating thickness of the low-voltage electric wire is smaller than that of a high-voltage electric wire, the windings can be evenly and closely wound, and the leak inductance can be thus reduced.