It is an object to provide a nucleating agent that is suitable for promoting crystallization of a crystalline resin and is derived from a natural product, in order to improve the moldability and the heat resistance of crystalline resins such as a poly(lactic acid) resin and a polyolefin resin; and to provide a crystalline resin composition including the nucleating agent. There is provided a crystalline resin composition including a crystalline resin and an amino acid metal salt; and a nucleating agent including the amino acid metal salt.