A middle leg (106b) of an E-shaped core (106) and one pair of outer legs (106a) and (106c) opposing each other via the middle leg are provided. A first pair of coils including at least two coils as a pair are wound around the middle leg (106b) so that a power transmission transformer unit is formed. The outer leg (106a) is divided into two outer leg portions (106aa) and (106ab) with a certain amount of space (106as) therebetween allowing coil wiring, and a second pair of coils including two coils as a pair are respectively wound around the respective two outer leg portions (106aa) and (106ab)so as to have mutually opposite winding directions, so that a signal transmission transformer unit is formed.