To reuse a fine slag as a substitute for crushed stone and crushed sand by separating and removing the fine slag included in a melted slag of waste.

On a cylindrical body 14 being freely rotatably supported in a posture inclined downward toward one end in the axial direction, an inlet 14a is formed on the upper side of the inclination and an outlet 14b is formed on the lower side of the inclination. A melted slag of waste is fed into the cylindrical body 14 through the inlet 14a and while a process wherein, after the melted slag of waste is moved form the bottom part side to the top part side with rotation of the cylindrical body, it falls down to the bottom part by its own wt. is repeated, the slag is moved toward the outlet 14b. Air is fed into the cylindrical body 14 from the inlet 14a and, in a process wherein the melted slag of waste falls down from the top part side of the cylindrical body 14, light fine slag is accompanied by air and is separated from other slag. Then, the air accompanied with this fine slag is exhausted to the outside of this apparatus through the outlet 14b.