Electromagnetic induction device

1. Field of the Invention An electromagnetic induction device having a flat configuration that requires a relatively small space for installation on a circuit substrate includes a flat bobbin (T) having a length (D) smaller than a radial size (D) thereof has primary and secondary windings () wound thereon. This bobbin (T) has coaxially aligned throughholes () defined therein into which core legs (T and T) of generally T-shaped first and second core pieces (T, T) are inserted from opposite directions, respectively. Respective core arms (T, T) of the first and second core pieces (T, T) extend parallel to each other.