To simply fix a toroidal core to an insulating cap in a short time by providing a protrusion having an elasticity at a bottom of a case of the cap, and providing engaging members at the case and a cover.

A common mode choke coil has a case 1 and a cover 4 made of a plastic, and a toroidal core 3 made of a magnetic material. The case has a protrusion 5 at its bottom and an engaging hole 7 at its side face. The cover 4 has an engaging pawl to be engaged with the hole 7 at its side face. The case 1 of the core 3 is fixed to the cover 4 by inserting to mount the core 3 on the protrusion 5 having the elasticity and provided at the bottom of the case 1, and engaging the case 1 with the cover 4 while retaining the core 3 with the cover 4. Thereafter, a winding is executed on an insulating cap, and then the common mode choke coil is obtained.