A transformer includes a magnetic core, a primary winding, and a plurality of secondary windings. The magnetic core has an axial and a radial direction. The primary winding includes a plurality of winding sections and at least one connecting section. The winding sections are arranged along the axial direction. The connecting section is connected between the two adjacent winding sections. Each of the winding sections includes a plurality of primary winding layers and pull-out portions. The primary winding layers surround the magnetic core and are arranged along the radial direction. One pull-out portion connects two primary winding layers adjacent to the pull-out portion. Part of normal projections of the primary winding layers on a surface of the magnetic core are located between normal projections of the pull-out portions on the surface of the magnetic core. The secondary windings surround the primary winding.