The object is to improve the adhesive force of an adhesive agent between an alginate impression material and a tray and ensure the steady adhesion between the alginate impression material and the tray. Specifically disclosed is an adhesive agent for the adhesion between an alginate impression material for dental applications and an impression tray, which comprises a polyamine compound having two or more amino groups in the molecule and a solvent. The polyamine compound is a polymer or a copolymer composing of aliphatic polyamine compounds, 3, 3-diaminobenzidine, or more than monomers of amino groups. The solvent is at least one selected from water, alcohols, acetone, and acetate esters. The polyamine compound is in an amount ranging from 1 part by mass to 50 parts by mass in an adhesive agent as 100 parts by mass.