Abstract: A method of manufacturing a cup-shaped coil assembly is described which employs a coil bobbin of a special design. The bobbin comprises a cylindrical member, a disc connected with one end of the cylindrical member to close it, a cap member detachably fitted into an opening in the other end of the cylindrical member, and a shaft disposed in alignment with the axis of the cylindrical member and having its one end attached to the disc and its other end slidably extending through the cap member. The method comprises the steps of assembling a coil bobbin in the manner mentioned above, and forming a coil around the bobbin by a skewed winding of wire, pressing the cap member into the cylindrical member, diametrically enlarging an opening formed at one end of the coil, and removing the cap member from the coil formed.