PURPOSE: To contrive to reduce the installation space by miniaturize the appearance by decreasing the weight and the amount of insulating oil, by a method wherein yoke cores provided each in the upper and lower surfaces of the main leg core are formed nearly triangular, and spaces are formed between the yoke cores and the inner peripheral surface of a tank, and a lead is arranged in the space.

CONSTITUTION: Three main leg cores 3 penetrates through a stud 6 and are clamped with clamping plates 23 and 24. Therefore, yoke cores 21 and 22, the clamping plates 23 and 24, etc. and a tank 20 are provided with an arc surface which is part of the inner peripheral surface of the tank 20 and with three arched spaces 25 at the linear part of the outer peripheral surface of the yoke cores 21 and 22, clamping plates 23 and 24, etc. Lead 10 for windings 9 are arranged each in these three spaces 25. This construction shapes the tank 20 cylindrical, miniaturize, and facilitates the production. On the other hand, the top of the tank 20 is provided with a pushing pocket 11 by corresponding to a lead 10, and a pushing 12 is installed to the top of the pushing pocket.