A transformer includes a primary coil unit including a primary winding, a first insulating portion and a shielding layer, wherein the first insulating portion wraps the primary winding, the shielding layer covers an outer surface of the first insulating portion, the shielding layer includes an opening, and a part of the first insulating portion is exposed at the opening; an outgoing wire terminal in the opening and having a first portion and a second portion connected with each other, the first portion coupled to the primary winding and wrapped by the first insulating portion, the second portion being exposed out of the first insulating portion; a connecting wire having a first end connected to the second portion of the outgoing wire terminal; and an insulating sleeve partially wrapping the connecting wire, and a second end of the connecting wire being exposed out of the insulating sleeve, (FIG. 17).