The deck side trim includes accommodating recesses in which left and right ends of a cover accommodating body are accommodated and disposed. A clamp portion provided at its side with an engaging pawl is provided in the accommodating recess. The clamp portion is provided with an inner hole having an opening at least on the accommodating recess side. A cap body for closing the opening is disposed in the inner hole. The cap body includes a cap leg and a cap head. When the cap leg of the cap body is fitted into the inner hole, the engaging pawl in the clamp portion is pushed outward, and the engaging pawl is engaged with the body engaging portion provided on the vehicle body.