An upper case manufacturing method using an axial draw mold, in molding of an upper case made of a synthetic resin and including an inclined cylindrical portion. A fixed mold is provided with a first half body, and a movable mold is provided with a second half body. The first half body and the second half body abut against each other in an inclined plane. The first half body has a first flat surface at both ends on the inner diameter side of the inclined cylindrical portion in the inclined plane, and the second half body has a second flat surface at both ends on the inner diameter side of the inclined cylindrical portion in the inclined plane. The first flat surface and the second flat surface are flat surfaces that prevent the occurrence of undercutting when the upper case is removed from an injection molding mold.