PURPOSE: To prevent molded insulating resin from leaking outside, passing through the gap between an anode lead and an insertion hole during the charge of the insulating resin into a flyback transformer, without using a thermoshrinking tube.

CONSTITUTION: An anode lead 3, which is pulled out of an insertion tube wall 4 and a insertion tube hole 5, with the insertion tube wall 4 of the anode lead 3 of the case of a transformer downward, is put between the clamp member 16 on the fixed side of a jig 8 consisting of split molds and the clamp member 17 on the movable side, and the gap 7 on the outlet side of the insertion tube hole 5 is blocked with the elastic pressure-welding forces of the clamp members 16 and 17. In this condition, the transformer case 1 is charged with insulating resin, and after hardening of the molded insulating resin, the clamp member 17 on the movable side is opened, and the molded flyback transformer is taken out of the jig 8 of split molds.