A guide block has a guide projection wall and a guide upper wall. The guide projection wall deviates from an end of a side-held portion in the folded-back state toward the start point of folding-back while moving toward a winding shaft along the longitudinal direction of a guide rail. The guide upper wall deviates in the direction orthogonal to a plane in which a shading sheet is unrolled and toward the shading sheet and abuts on the side-held portion being unfolded while moving toward the winding shaft along the longitudinal direction of the guide rail.