PURPOSE: To enable to employ a split mold structure as a mold of a coil bobbin by forming collars at both ends of a winding body formed with a bent piece for forming square-sectional cylinder by bending and coupling with both open ends in U-shape.

CONSTITUTION: Collars 12, 13 are respectively formed at both ends of a winding body having bent pieces 10, 10' for forming square-sectional cylinder by projecting upward and bending perpendicularly at both open ends in U-shape. Further, a terminal unit 15 to which terminal pins 14 are implanted is provided at the lower ends of the collars 12, 13. The pieces 10, 10' are bent and coupled with a coil bobbin 9, and a winding is then wound on the body 11 between the collars 12 and 13. E-shape and I-shaped cores 18, 19 made of ferrite core or laminated core are associated with the bobbin 9 to construct a transformer.