An object of the invention is, in producing a cast molded article by crosslinking a water-dispersed urethane prepolymer with a polyamine compound, providing a method for producing a cast molded article made of a polyurethane porous substance in which a cured reactant has good demolding properties and a cast molded article with a fine structure can be easily produced, and a cast molded article having a fine structure with high dimensional accuracy. The cast molded article of this invention is produced by reacting polyol, a chain length regulator, isocyanate and 0.1 through 4 wt % of a hydrophilic chain length regulator to one another, allowing a resultant urethane prepolymer having a terminal isocyanate group to be mixed with and dispersed in water, mixing a resultant water-dispersed urethane prepolymer with 1,4-diaminobutane and injecting a resultant mixture into a die for crosslinkage, and demolding a resultant cured reactant and removing moisture from the cured reactant.