A guide rail comprises a front passage forming member (23F) and a rear passage forming member (23B) that are two passage forming members mutually facing that sandwich an outer edge (13E) of a shielding material (13). At least one of the two passage forming members is a movable part that moves, in a space between the two passage forming members, between a first position that allows lifting and lowering the outer edge (13E) of the shielding material (13) and a second position for which the pressing pressure on the outer edge (13E) of the shielding material (13) is higher than the first position. The movable part is disposed in a location that can be in contact with the shielding material (13) that is deviating from the space between the two passage forming members, and moves from the first position to the second position by following the shielding material (13) that is deviating from the space.