Water-insoluble nigrosine compound which is a salt of nigrosine with sulfuric acid and/or phosphoric acid, crystalline resin composition containing the nigrosine compound, and fiber-reinforced crystalline resin molded product comprising a crystalline resin and a fibrous reinforcing material and the nigrosine compound both contained therein, wherein the surface gloss is higher than that of the fiber-reinforced crystalline resin molded product with nigrosine as a substitute for said nigrosine compound. Methods for lowering the crystallization temperature of a crystalline resin, improving the fluidity of a crystalline resin, and improving the surface gloss of a crystalline resin, by incorporating the water-insoluble nigrosine in the crystalline resin respectively.