A transformer is configured to include a pair of cores and that each have an inner leg, wherein a primary winding that is wound around a bobbin having a hollow into which the inner legs of the cores and are inserted, and a secondary winding that has a hollow into which the inner legs of the cores and are inserted and that is constituted of a conductor formed by die-cutting a metal plate into a ring, are dispersedly arranged over the inner legs of the cores and. The bobbin has bobbin support portions that come into contact with a surface of a printed circuit board on which the transformer is implemented.