In order to maximally reduce deviation arising between the center axis of the wire covers and the center axis of the wire leading-out holes in a state in which the wire covers are press-fitted into the corresponding wire leading-out holes, it is desirable to adopt a configuration in which force acts equally on the plurality of crush ribs formed in the head parts of the wire covers during press-fitting of the wire covers into the corresponding wire leading-out holes. Therefore, at least portions of the wire covers at which the crush ribs are provided, and at least portions of the wire leading-out holes at which the portions where the crush ribs are provided to the wire covers are press-fitted, are preferably formed so that the contour shapes of the horizontal cross-sections in each section along each of the axial directions have N-fold symmetry (where N is an integer equal to or greater than 2) with respect to the respective center axis.