To provide a voltage adjusting machine using a variable-winding-number transformer, which is made to have a lifetime of 30 years, of about 6,600V and 1,000 KVA by making a conventional variable-winding-number transformer 1/2 in weight, less than 1/400 in spark, and about 50 times in maximum manufacturable winding capacity.

A voltage is adjusted by rotating simultaneously in same direction two rotating spools fitted to legs of a core type transformer to mutually moving windings of the spools. Each winding is formed by putting belt-like conductors one on another to minimize bending and stretching of curing, and a large current is allowed to flow, and annular coils or current collecting rings are fitted to a frame so as to collect a current from a rotary portion to a fixed portion, and brushes are brought into contact with them.