According to one embodiment, a contactless power transfer transformer includes a both-sides wound coil. The both-sides wound coil includes an inter-magnetic-pole core portion between two magnetic pole portions. The winding wire is wound around a wound region of the inter-magnetic-pole core portion. The inter-magnetic-pole includes: a plurality of separate magnetic members that connect to each of the two magnetic pole portions, and are arranged with a spacing therebetween and in parallel with each other; and a heat conductor that is alternately arranged with respect to the separate magnetic members on a plane formed by the separate magnetic members so as to be in contact with the separate magnetic members. Heat generated by the separate magnetic members is guided to the outside of the wound region of the inter-magnetic-pole core portion through the heat conductor, and is dissipated.