PURPOSE: To eliminate the need for a clamping ring or the like of a high-voltage transformer such as a fly-back transformer as well as to maintain the uniformity of the performance by securing one of the junctions of a pair of U-shaped cores of the transformer by means of a coil coated with molded thermosetting resin and holding the other by means of a compression ring.

CONSTITUTION: The magnetic path formed by a pair of U-shaped cores 11 and 12 penetrates a coaxial coil 10 having a tube case portion 13 that projects upwards and low- and high-voltage coils and bobbins coated with molded thermosetting resin. On the other hand, the ends of the pair of cores 11 and 12 facing each other at a junction 14 on the side not penetrating the coil 10 are fitted with a compression ring 15, as shown, so that the cores 11 and 12 contact with each other with a slight elasticity. The ring 15 performs functions of a guide when the pair of cores are bonded, and keeping the elasticity of the cores. This eliminates the need for a clamping ring or the like, and permits the uniformity of the performance to be maintained.