A case 12 of a transformer 10 formed in such a manner that a transformer body 13 is accommodated in the case 12 having a rectangular-parallelepiped shape and a resin 14 is filled therein and solidified is configured such that the case 12 has one open face, and side faces 22a, 22b, 22c and 22d located at borders of the opening is partially removed, and tape is attached to cover the removed portions 23a, 23b, 23c and 23d. With this configuration, since the tape which is sufficiently thinner than the case forms side faces at the removed portions, gap between the transformer body and the case hard to be reduced. Accordingly, the resin is allowed to easily enter therein and air bubbles can be completely removed.