Abstract: A spiral gasket apparatus, capable of being held on an inclined flue gas outflow pipe without falling off therefrom, is constructed by winding a metal hoop member and a filler member, superposed on each other. A part of the hoop member from the beginning extremity of the hoop member on the inner side, which is wound as many as several turns to a welded fixed portion thereof, is raised inward by using the welded fixed portion as a fulcrum. An extremity portion thereof is folded back to form a superposition part. Since the raised part of the hoop member acts as a spring and is brought elastically into contact with an inclined flue gas outflow pipe, the gasket is held on the flue gas outflow pipe.