A polyglycidyl ether compound having a plurality of epoxy groups and a hydroxy group in the molecule is reacted with a silane coupling agent having an isocyanate group, and specifically the hydroxyl group on the polyglycidyl ether compound is reacted with the isocyanate group on the silane coupling agent. Then an organosilicon compound having a plurality of epoxy groups per alkoxysilyl group is synthesized wherein the ratio of epoxy groups to alkoxysilyl groups may be adjusted as desired. The resulting organosilicon compound is useful as a primer and resin modifier.