PURPOSE: To carry out mounting of a lightweight plastic film with facilitated anchoring and pulling off and good reliability, by sandwiching and fixing the plastic film between a wiry material of a frame peripherally provided with hollow helical molded bodies and fixtures having a cylindrical engaging part.

CONSTITUTION: Hollow helical molded bodies 7 (e.g. consisting of galvanized steel wire) are peripherally provided on a straight wiry material 4 of a tunnel frame. The end of a plastic film 15 is sandwiched and mounted between the above-mentioned hollow helical molded bodies 7 and fixtures 10 having a cylindrical engaging part with an inside diameter almost equal to the outside diameter thereof. Demounting is simply carried out in the same manner as in mounting and related materials are miniaturized to facilitate transportation.