PURPOSE: To obtain a crosslinking agent which gives a tough and highly acid- resistant cured coating film of three-dimensional network structure when heat together with a base resin having active hydrogen atoms.

CONSTITUTION: This crosslinking agent comprises a compound containing active hydrogen atoms and represented by the formula (wherein A is a 6-10C aromatic hydrocarbon group, a 4-8C alicyclic hydrocarbon group, a biphenyl group or a 2-6C aliphatic hydrocarbon group; R1 and R2 are each independently H, 1-2C alkyl or 6-20C aryl; and n is an integer of 2 to 10).