Provided is the one-pack type backing resin composition which exhibits excellent fall-off resistance, excellent storage stability, and high flame retardancy. A one-pack type backing resin composition includes 100 parts by mass of (A) a (meth)acrylic polymer, and 50 to 500 parts by mass of (B) a flame retardant, the (meth)acrylic polymer (A) being produced by emulsion polymerization of a monomer component, and having a solvent-insoluble content of 0 to 85 mass %, the monomer component including 0.5 to 25 mass % of (a) glycidyl methacrylate, 0.2 to 10 mass % of (b) an unsaturated carboxylic acid monomer, and 70 to 99.3 mass % of (c) an additional copolymerizable monomer (provided that (a)+(b)+(c)=100 mass %).