To avoid increase in a volume and restrain cost by arranging a member for increasing elastic force in accordance with temperature rise at a junction part of a core in a transformer.

A transformer 1 has a hollow part and is constituted by a coil 4 wound on the outer circumference of a bobbin 3 having terminal pins 2, an E-shaped magnetic substance 5, an I-shaped magnetic substance 6, a member 7 such as a vulcanized rubber having a characteristic such as to increase the elastic force in accordance with temperature rise, and an elastic supporting metal fitting 8 for holding and fixing the magnetic substances 5 and 6 in a direction of close contact with each other. Also, two magnetic substances forming a core have the same E-shape, and an elastic member inserted in a center part of three junction parts of the magnetic substances is removed to form an air gap, that is, a cavity.