A method of imparting flame retardance to at least one resin comprising adding to said resin a compound containing a phosphoric ester represented by the formula (I): wherein R1 and R2, the same or different, are an alkyl group having a carbon number of 1 to 6 and R3 is an alkyl group having a carbon number of 1 to 20, and wherein the resin comprises a polyurethane resin. 2.