A slim-type high voltage transformer includes a case, and a transformer portion configured by mounting at least primary and secondary winding coils wound in the shape of a rectangular or elliptic track to protruding grooves formed in the interior of the case and then mounting a first copperplate core on the primary and secondary winding coils. In the transformer, the transformer portion further includes an insulating member interposed between the primary and secondary winding coils and the first copperplate core. Accordingly, a bobbin for winding a coil is not used, so that the height of the transformer can be minimized, thereby decreasing the size of products. Also, a winding is divided into two sections to be molded, so that the insulation and heat generation of the winding can be effectively controlled, thereby improving the stability of the transformer.