As illustrated in FIG. 13 and FIG. 14, screw holes 35 that penetrate the housing section 30 along the front-rear direction are formed in the rim of the opening 31 of the housing section 30. Screws 36 are inserted from the front-face side of the rack 10 into the through holes 67 of the positioning pieces 65, and the screws 36 are screwed into the screw holes 35 formed in the rim of the opening 31 of the housing section 30 so as to fix the positioning pieces 65 in a state abutting the rim of the opening 31 of the housing section 30.

For example, in cases in which length L1 is longer than length L2, the second main wall 56 of the cable unit 50 abuts the end wall 32 of the housing section 30 from the front-face side of the rack 10, and the positioning pieces 65 of the first main wall 54 may be spaced apart from the rim of the opening 31. In such cases, when the screws 36 are screwed into the screw holes 35, the positioning pieces 65 are pushed in toward the housing section 30 side by the heads of the screws 36, such that the first casing body 52 slides toward the back-face side of the rack 10 relative to the second casing body 53 and the casing 51 contracts in the front-rear direction. Accompanying sliding of the first casing body 52 toward the back-face side of the rack 10, the positioning pieces 65 are abutted against the rim of the opening 31 from the front-face side of the rack 10 and the positioning pieces 65 are fixed to the rim of the opening 31.