To improve the grounding property of the mounting of a transformer on a board and prevent the continuity failure of its mounting solder, by making spring-form one-portion of each terminal of its bobbin, and by making thin one-portion of each terminal so as to have a spring property.

A transformer comprises a bobbin 3 with wound coils and a core 6 comprising laminated E-shaped thin plates made of permalloy, etc., in the direction of their thickness. The bobbin 3 comprises a cylindrical winding core whereon the coils are wound, flanges provided at both the ends of winding core, and terminals 5 implanted in one-ends of the flanges. As a result, each terminal 5 is expanded and contracted easily, and is made deformable by the weight of the transformer itself. Also, since one-portions of the terminals 5 are made spring-form, the grounding property of the transformer on a board can be improved.