To make it possible to satisfy the request in the technical field relating to the release of volatile org. compds. by incorporating carbon supply sources selected from a group of activated carbon, activated graphite and a mixture composed thereof into additives.

The carbon supply sources selected from the group of the activated carbon, the activated graphite and the mixture composed thereof is incorporated into the additives for molding sand. Pulverized ore contg. compds. selected from a group consisting of humic acid, the metal salt of the humic acid and the mixture composed thereof and the carbon supply sources selected from the group consisting of the carbon, graphite and the mixture composed thereof are incorporated into the additives for the molding sand in the amts. of 5/95 to 95/5 as the weight ratio the pulverized ore/the carbon supply sources. As a result, the gases of the volatile org. compds. are captured in the activated carbon and/or the graphite.