PURPOSE: To contrive miniaturization and lightening of a transformer by arranging a coil supporting fitting inside an outer casing to reduce the sizes of contents, resulting in reduction of sizes of the whole body of the transformer.

CONSTITUTION: A coil supporting fitting 9 is fixed to an iron core fixing fitting 1. A fixing fitting 8 for the supporting fitting is fixed unitarily to the iron core fixing fitting 1 by welding or the like and is clamped to be fixed between a coil 5 and the supporting fitting 9 through an insulator 4 for supporting the coil by a fixing bolt 3. Thus the supporting fitting 9, the fixing fitting 8 and the threaded part of the bolt 3 do not jut forth outside of the outline of the iron core fixing fitting 1 so that sizes of the inside of the tank can be minimized, resulting in the miniaturization and lightening of the transformer.