PURPOSE: To make the line simple and treatment easier by treating the refuse separated in a waste sand washing line in a sludge treating line, and treating the waste sand separated in the sludge treating line in the waste sand washing line.

CONSTITUTION: The refuse carried out in a waste sand washing line A is supplied to a sludge treating line B and is thereby treated. Sepcifically, the refuge g3 which has been removed in a coarse separating process (a), is relatively coarse and is stuck with sludge etc. is supplied to the washing device 23 of the line B and a bit of refuge g4 which is carried out from an agitating and washing process (b) such as cyclone and is discharged together with waste water etc. from a discharge pipe 9 is separated in a separator 27 such as vibration sieve, and this is supplied to a dehydrater 24 and is thereby treated. On the other hand, the screenings treated in the sludge treating line B are treated in the washing device 23. The waste sand S0 separated and removed at this time is supplied to the agitating and washing process (b) of the waste sand washing line A, where it is washed together with the waste sand supplied from the carry-out machine 6.