An axial end portion of a dielectric sheet, which is wound around a central core of an ignition coil, includes an axially projecting portion, which projects from an axial end surface of the central core positioned radially inward of primary and secondary coils in a case. An inner peripheral side axial end corner and an outer peripheral side axial end corner in the axially projecting portion are respectively formed into a blunt smooth round shape. Dielectric resin is filled in spaces in the case. Alternatively, the axially projecting portion may have a folded end portion, which includes a plurality of generally arcuate segments folded one after another on one circumferential side thereof.