In order to additionally furnish the transformer with the reactor capability easily without having to change the structure of the transformer, a transformer is formed by winding an input-side coil 1b and output-side coils 1a and 1c around a shell-type iron core 2 so that voltages are induced in the output-side coils 1a and 1c by magnetic fluxes generated by a voltage applied on the input-side coil 1b, and two reactor coils 3a and 3b having the same winding number in the opposite winding directions and making a pair are wound around the shell-type iron core 2. A shared reactor transformer as a whole is thus formed.