Provided is an additive that increases or improves a light resistance of anon-fluorinated thermoplastic resin (e.g., a super engineering plastic, such as an aromatic polyamide, a liquid crystal polyester, or an aromatic polyetherketone resin). The additive comprises a fluorine-containing resin. The fluorine-containing resin may be, for example, a fluorine-containing resin comprising a tetrafluoroethylene unit as a monomer unit, in particular, may be a tetrafluoroethylene copolymer (e.g., at least one member selected from the group consisting of a copolymer of tetrafluoroethylene and another fluorinated olefin, a copolymer of tetrafluoroethylene and a fluorinated vinyl ether, and a copolymer of tetrafluoroethylene, another fluorinated olefin and a fluorinated vinyl ether).