A reinforcing sheet for a resin molded article comprising: a constraining layer and a reinforcing layer laminated on the constraining layer, wherein the reinforcing layer is formed of a thermally adhesive type adhesive composition, the thermally adhesive type adhesive composition contains a hydrogenated polymer of a monomer containing conjugated dienes and a copolymerizable monomer which is copolymerizable with the conjugated dienes, and a tackifier, the mixing ratio of the copolymerizable monomer is 15 to 50 parts by weight with respect to 100 parts by weight of the conjugated dienes, the tackifier contains an alicyclic saturated hydrocarbon resin and a terpene resin, the constraining layer is one kind selected from the group consisting of a glass cloth, a resin impregnated glass cloth, a non-woven fabric, a metal foil, a carbon fiber, and a polyester film, and when the reinforcing sheet for a resin molded article is attached to a polypropylene plate having a thickness of 2.0 mm and is heated at 80°C for 10 minutes, the bending strength at a displacement of 1 mm of the resulting sheet after the heating is 3 N or more and the maximum bending strength thereof is 30 N or more, and a high-temperature adhesion retention ratio R as determined by the following formula is 80 % or more. High-temperature adhesion retention ratio R = (Adhesive force A 1000h after heating at 100°C for 1000 hours / Adhesive force A 1h after heating at 100°C for 1 hour) x 100 Adhesive force A 1000h after heating at 100°C for 1000 hours: the adhesive force with respect to a polypropylene plate, which is obtained by attaching the reinforcing layer to the polypropylene plate to be heated at 80°C for 10 minutes and then heated at 100°C for 1000 hours to be thereafter measured by a 90-degree peeling test based on JIS Z0237 (in 2000) at a peeling rate of 300 mm/min. Adhesive force A 1h after heating at 100°C for 1 hour: the adhesive force with respect to a polypropylene plate, which is obtained by attaching the reinforcing layer to the polypropylene plate to be heated at 80°C for 10 minutes and then heated at 100°C for 1 hour to be thereafter measured by a 90-degree peeling test based on JIS Z0237 (in 2000) at a peeling rate of 300 mm/min. a constraining layer and a reinforcing layer laminated on the constraining layer, wherein the reinforcing layer is formed of a thermally adhesive type adhesive composition, the thermally adhesive type adhesive composition contains a hydrogenated polymer of a monomer containing conjugated dienes and a copolymerizable monomer which is copolymerizable with the conjugated dienes, and a tackifier, the mixing ratio of the copolymerizable monomer is 15 to 50 parts by weight with respect to 100 parts by weight of the conjugated dienes, the tackifier contains an alicyclic saturated hydrocarbon resin and a terpene resin, the constraining layer is one kind selected from the group consisting of a glass cloth, a resin impregnated glass cloth, a non-woven fabric, a metal foil, a carbon fiber, and a polyester film, and when the reinforcing sheet for a resin molded article is attached to a polypropylene plate having a thickness of 2.0 mm and is heated at 80°C for 10 minutes, the bending strength at a displacement of 1 mm of the resulting sheet after the heating is 3 N or more and the maximum bending strength thereof is 30 N or more, and a high-temperature adhesion retention ratio R as determined by the following formula is 80 % or more. High-temperature adhesion retention ratio R = (Adhesive force A 1000h after heating at 100°C for 1000 hours / Adhesive force A 1h after heating at 100°C for 1 hour) x 100 Adhesive force A 1000h after heating at 100°C for 1000 hours: the adhesive force with respect to a polypropylene plate, which is obtained by attaching the reinforcing layer to the polypropylene plate to be heated at 80°C for 10 minutes and then heated at 100°C for 1000 hours to be thereafter measured by a 90-degree peeling test based on JIS Z0237 (in 2000) at a peeling rate of 300 mm/min. Adhesive force A 1h after heating at 100°C for 1 hour: the adhesive force with respect to a polypropylene plate, which is obtained by attaching the reinforcing layer to the polypropylene plate to be heated at 80°C for 10 minutes and then heated at 100°C for 1 hour to be thereafter measured by a 90-degree peeling test based on JIS Z0237 (in 2000) at a peeling rate of 300 mm/min.