An unsaturated polyester resin composition includes aluminum hydroxide and a resin component containing an unsaturated polyester, a polymerizable monomer, and a low profile agent. The unsaturated polyester is a polymerized product of polybasic acid and polyhydric alcohol. The polybasic acid contains unsaturated polybasic acid, and the unsaturated polybasic acid is blended in an amount of 80 mol % or more relative to 100 mol % the polybasic acid. The low profile agent contains polyvinyl acetate, and the polyvinyl acetate is blended in an amount of 3 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the resin component. The aluminum hydroxide is blended in an amount of 150 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the resin component.