A step is formed in at least a portion of the outer edge of the frame member 11 that constitutes a portion of the first case body 10. Specifically, step portions 15 that recede so as to be lower than the bottom faces of the first channel portions 61 (the bottom faces of the first portions 611, the second portions 612, and the space portions 613) are formed. Also, support protrusions 14, which are protrusions that project upward, are formed on the frame member 11 that constitutes a portion of the first case body 10. The upper surfaces of the support protrusions 14 serve as the base portions 12. The lock protrusions 141 that project outward are formed on the outer faces of the support protrusions 14. The outer faces of the support protrusions 14 are planar (flush) with the surfaces of the step portions 15 that extend in the up-down direction. In a view from the side, grooves (transverse grooves 613a) are formed in the frame member 11 by removing portions of the base portions of the support protrusions 14. These transverse grooves 613a are portions of the space portions 613 (see FIGS. 2, 6, and the like).