To make the cooler itself compact and to improve the control accuracy of the temp. of recovered molding sand by bringing the apex of an agitating vessel into tight contact with the base of a dust collector to shut off the inside of an agitating vessel from the atm. at the time of ascending of an agitating unit.

A suction port 7a of the bore smaller than the bore of the feed and discharge port 3a of the agitating vessel is opened at the base of the dust collector 7. The agitating unit 6 ascends after the acceptance of the recovered molding sand. While the recovered molding sand in the agitating vessel 3 is kept agitated by driving an agitating shaft rotating means 5 in the state of the apex of the agitating vessel 3 held into tight contact with the base of the dust collector 7 via a sealing material, a suction means 8 is activated to successively reduced the pressure in the agitating vessel 3 through the suction port 7a of the dust collector from the feed and discharge port 3. As a result, the agglomerated sand grains in the recovered molding sand are loosened and the moisture on the sand grain surfaces is sufficiently evaporated. The molding sand may be mingled without unevenness even if charging of the molding sand and water spraying are simultaneously executed and, therefore, the entire part of the recovered molding sand may be effectively and uniformly cooled by the latent heat of evaporation.