Provided are an organic binder for a mold, which can advantageously extend the pot life without causing uneven curing, reduction in mold strength and an increase in the amount of use of a catalyst; a molding sand composition which is obtained by using the organic binder for a mold, and which exhibits an extended pot life; and a mold produced by curing such a molding sand composition through gas hardening. The urethane-curable type organic binder for a mold, which is used for production of a urethane-based mold, is constituted by comprising a specific alkoxysilyl group-containing ketimine compound, together with a polyol compound and a polyisocyanate compound.