The invention relates to a transformer with a tap changer, wherein optionally the primary or secondary side can be regulated by the tap changer, and wherein, on the side of the transformer to be regulated, a main winding and at least one regulating winding, which is connectable by the tap changer, are provided. According to the invention, the main winding is divided into two main winding parts, and the at least one regulating winding and the tap changer (3) connecting the regulating winding are arranged electrically between the two main winding parts (1, 2).