PURPOSE: To obtain a three-winding Scott connecting transformer being small- sized and enabling the reduction of manufacturing cost, by adding a tertiary winding to a Scott connection transformer and by disposing a primary winding between a secondary winding and the tertiary winding.

CONSTITUTION: A main transformer is formed by providing a core leg 12 with a secondary winding 14 for the main, a primary U terminal side winding 15, a primary W terminal side winding 16 and a tertiary winding 17 for the main, concentrically and sequentially from inside. A teaser transformer is formed by providing a core leg 13 with a secondary winding 18 for a teaser, a primary V terminal side winding 19 and a tertiary winding 20 for the teaser concentrically and sequentially from inside. The primary windings 15, 16 and 19 are connected together by a node M. As for the insulation degree of the secondary windings and the tertiary windings, it may be a half of a conventional one, since each one end Nu1, Nu2, Nv1 and Nv2 thereof is grounded invariably in working. In addition, a dimension G4 between the winding 18 and the winding 19 is made larger than a dimension G5 between the winding 19 and the winding 20, so as to reduce a leakage impedance between the primary windings of the main transformer.