A transformer is provided having good workability during production and good connection of the secondary main coil and the primary supportive coil. The transformer has a bobbin with a base part and first hollow cylinder part with a first through hole and a core projecting in a first positive direction from said base part, and a case having an upper collar part formed with a primary main coil wound around said first hollow cylinder part, a second through hole leading to said first through hole, and a second hollow cylinder part formed at the outer peripheral face. Said primary main coil is housed and projects in a first negative direction from said upper collar part. A lower collar part opposes said base part by extending approximately parallel to said mounting face. The primary supportive coil and secondary main coil are wound around said first and second sections, respectively.