In a large-sized radiator core support manufactured by filling a mold cavity 2 with a resin material through injection, polypropylene (PP) containing carbon fiber in a range of 15 to 30 wt % is used as the resin material, and an average fiber length of the carbon fiber remaining after molding is set to 1.5 mm or more. Moreover, a spiral flow length L/D of the carbon fiber is set to 200 mm or more.