To obtain a core which is easy to assemble, additionally does not generate distortion of a thin plate while inserting into a bobbin and does not generate a defective property by forming several layers of the end of the core butting short leg sheets thinner than terminal forming sheets.

A transformer is constituted of a bobbin on which a coil is wound and a core comprising an E shape thin plate made of Parmalloy and so on being laminated in the thickness direction. The core 61 used for the transformer is constituted of a thin sheet 1 having a long leg at a lower part being laminated and a thin sheet 4a having a short leg and a same length at the upper part being combined. Therefore, hitting a bobbin inserting port or the terminal can be prevented at the upper part of the bobbin. The core is constituted of thin sheets having long legs at the lower part being laminated and thin sheets having short legs and different lengths at the upper part being combined. Thus, the transformer is easily assembled further does not generate distortion of the thin sheets and does not generate a defective property when inserting into the bobbin.