Provided is a mold organic binder that exhibits an excellent fast curing property and can shorten the molding time when a mold is manufactured through ordinary temperature curing.ã¿¿The mold organic binder used to mold a phenolic urethane-based gas-curing mold or a self-curing mold is formed using, as essential components, a phenol resin, an organic solvent, and a reaction product of i) a polyisocyanate compound and ii) a compound a having two or three intramolecular hydroxyl groups and/or carboxyl groups and having a number average molecular weight of 300-3000, the proportion of the compound a in relation to the polyisocyanate compound being 0.1-12.0 mass%.