PURPOSE: To simplify the circuit of the subject transformer by a method wherein the common terminals of the plurality of change-over switches electrically independent with one another are connected to a plurality of windings which are serving as parallel shunts using a single-phase unit based on a three-phase unit to be used for a delta connection.

CONSTITUTION: A tap 12 consists of an odd tap 12-1 and an even tap 12-2 is provided with a transformer winding 11, and these taps are connected to change- over switches 14 and 14' through the intermediary of a selector 13. And each common terminal of the change-over swiches 14 and 14' which are electrically independent with each other are connected to splitted windings 15 and 15' which constitute parallel shunts. Thus the branching off of the change-over switches can be secured without splitting the tap wirings. As a result, the tap selector 13 functions with one stage only and the tap winding is unnecessary to split, thereby enabling to reduce the tap lead wires and to simplify the circuit.