To selectively separate histamine from a sample containing both histamine and histidine by using the histamine as a template molecular and polymerizing a functional monomer under coexisting with a cross-linking monomer.

For synthesizing this histamine receptor polymer, a cross-linking monomer that can polymerize a functional monomer that has an interaction with histamine and is capable of polymerization with a cross-linking reaction is required. As a material, a device, and a polymerization condition that are required for synthesizing, the histamine is used as a template molecule, and same as that is synthesis of an imprint polymer is used. Ionic bond or inter- molecular bond is preferred as the interaction, acrylic acid or methacrylic acid is used as a functional polymer, and preferably, the methacrylic acid is used at a ratio of 1-100 mol to 1 mol histamine. Ethyleneglycoldimethylacrylate is preferable as the cross-linking monomer, and radical polymerization is suitable as the polymerization reaction.