To provide a joining sheet for cylindrical heat reserving material, which allows operations to be surely and simply processed even if a gap between the cylindrical heat reserving material and the wall surface or the ceiling, is narrow, and is hardly disintegrated even if the heat reserving material is extended/contracted.

In a joining sheet to be wound over the outer circumference of cylindrical heat reserving material, the aforesaid joining sheet is formed out of a waterproofing outer layer 11, an inner layer 15 composed of a foamed body laminated to the one surface of the outer layer, and of a self pressure sensitive adhesive 19 provided for the surface of the inner layer, and the winding surface of the joining sheet is formed into a recessed and projection part 22.