A transformer includes a main body, at least a rubber piece and a wire-guiding groove. The main body has a primary winding partition, several secondary winding partitions and two end portions. Several leads are disposed in either end portion. The rubber piece provides the buffer action, and it makes the secondary wire of the transformer which is pulled from several primary leads run closely and automatically fitted on the surface of the rubber piece and the primary end piece. The transformer used the rubber piece as buffer to avoid bending and breakage. The wire-guiding groove is formed in the primary end piece. The wire-guiding groove can guide the secondary wire to keep the secondary wire running closely and neatly on the lower surface of the primary winding partition.