Protein crystallizing method using a protein crystallizing agent and protein crystallizing agent

To provide a technique which can be crystallized with high probability a desired protein (protein crystallizing agent and a protein crystallizing method). Also provides a technology (screening methods and protein crystallization screening reagent of crystallization conditions of protein) to determine easily and efficiently crystallization conditions of the protein. As protein crystallizing agent, basic amino acids, as acidic amino acid, or using at least one compound selected from the group consisting of amide derivatives of ester derivatives and amino acids, or protein crystallizing agent, the at least one compound and used in combination with other protein crystallizing agent.