PURPOSE: To enhance sorting work efficiency, by a method wherein the heights of the side walls of a sorting table is made low toward the outlet side thereof to permit a light wt. substance to get over the side walls certainly and easily.

CONSTITUTION: The side walls 1b, 1c of a sorting table 1 are formed so as to be high at the inlet side 1X of the sorting table 1 and become lower toward the outlet side 1Y thereof in a definite inclination. By this structure, because a light wt. substance such as compost gets over the side walls certainly and easily even in the vicinity of the outlet side of the sorting table 1, sorting work efficiency is enhanced while potential difference between an electrode plate and the sorting table 1 can be lowered and power consumption can be reduced.