PURPOSE: To remarkably enhance the adhesive strength of a rubber with a reinforcing material, by using an adhesive consisting of a combination of a specified methylene acceptor and a specified methylene donor.

CONSTITUTION: A compound of formulaI(wherein each of R1, R2 is H, a 1W 12C alkyl group or a 6W12C aryl group), e.g., phenol or cresol, and a compound of formula II (wherein X is -OH, -NH2, a group of formula III, -OR4; each of R3, R4 is a 1W4C alkyl group), e.g., resorcinol, are brought into reaction at a molar ratio of 25/75W75/25 to obtain a co-condensation resin. Then, a salt of resorcinol or phenol and hexamethylenetetramine is mixed with the resin to prepare a vulcanization adhesive. By using the adhesive, a rubber and a reinforcing material consisting of nylon cords are bonded to each other with vulcanization.