PURPOSE: To improve the dispersibility of magnetic particles while maintaining the mechanical characteristics of polyester resin or polyurethane resin as a binder by using polyester resin or polyurethane resin prepd. by reacting a specified phosphorus compound.

CONSTITUTION: The dispersibility of magnetic particles in a magnetic recording medium is improved while maintaining the mechanical characteristics of polyester resin or polyurethane resin as a binder by using polyester resin or polyurethane resin prepd. by reacting a phosphorus compound having an ester forming functional group. The phosphorus compound is represented by the formula, and it is used so that 500W40,000ppm phosphorus atoms are contained in the resin. In the formula, R1 is a univalent ester forming functional group; each of R2 and R3 is a 1W10C univalent hydrocarbon group, halogen or a univalent ester forming functional group; A is a bivalent or tervalent org. residue; n1 is 1 or 2; and each of n2 and n3 is an integer of 0W4.