To provide a set-up transformer and an electric device using the same by which the reduction of size in thickness, downsizing and cost reduction can be realized.

Two core members 29 and 30 provided with a same shape and first, second and third magnetic legs arranged in order are laminated in reverse direction with each other so as to form a core, and the second bar of two core members is inserted into the cylindrical part of a bobbin which is wound by primary and secondary windings, thereby constituting a set-up transformer. Therefore, the number of core members as well as the kind of parts can be reduced, and the reduction of size in thickness, downsizing and cost reduction can be also realized.