PURPOSE: To facilitate the leading-out of a low secondary voltage and improve voltage regulation, by making the electromotive force of one turn of a primary winding differ from that of a secondary winding.

CONSTITUTION: In a magnetic circuit constituted by dividing the total magnetic flux part 5 into two or more parts, a primary winding 1 is wound for the total flux 5, and secondary windings 2, 3 are wound for the divided magnetic circuits. The electromotive force V2/T of one turn which is generated in the secondary winding 2 or 3 is set smaller than the electromotive force V1/T of one turn of the primary winding 1. The secondary windings 2, 3 are independently used or connected in parallel or connected in series, thereby facilitating the leading- out of a secondary output voltage. Hence, in a transformer whose electromotive force of one turn is high, the design and the manufacturing of the low voltage output of the secondary side are facilitated. That is, the setting of the secondary output voltage is facilitated by the loading inversely proportional to the loads of one or more secondary widings or by exciting the primary and the secondary winding magnetic flux in the rectangularly twisted directions, so that constant voltage operation can be simply realized.