PURPOSE: To provide a device capable of solidifying molten slag discharged from a waste melting and processing furnace into small blocks through air cooling so as to facilitate a reutilization of solidified item and eliminate cooling water.

CONSTITUTION: There is provided a conveyor in which a plurality of shallow pans 8 are set adjacent to each other from an upper horizontal path for going to a lower horizontal path for returning so as to be continuously arranged, and each of the pans is circulated while its upward horizontal position being kept from the horizontal path for going to the horizontal path for returning. The horizontal going-path of the conveyor is provided with a discharging port 20 of a waste melting and processing furnace for dropping the molten slag 21 into the pans 8 is installed in the horizontal going-path of the conveyor. In addition, there is provided a reversing mechanism 25 for reversing the pans 8 and discharging the solidified material of the molten slag 21 solidified in the pans 8 in the horizontal returning-path of the conveyor.