PURPOSE: To provide the device for treating a waste etching liquid which automatically and exactly manages a reduction treatment process for the waste etching liquid.

CONSTITUTION: The waste etching liquid formed after copper is etched with, for example, ferric chloride etching liquid in a reduction reaction chamber 2 is subjected to a reduction treatment and the cuprous chloride in the waste liquid is recovered as copper metal and a ferrous chloride soln. is supplied to a recovering means 6 where this soln. is recovered as a ferric chloride etching liquid. On the other hand, the soln. in the reduction reaction chamber 2 sampled by a sampling means 3 is adjusted by addition of a reducing agent for reducing the copper ions in the soln. to univalent copper ions and a color developing agent, etc., and thereafter the concn. of the univalent copper ions in the soln. is detected by an absorptiometry in a measuring means 4. A control signal is outputted from a control means 5 in accordance with the detected value and, for example, the stagnation time of the soln. in the reduction reaction chamber 2, etc., are controlled, by which the management of the reduction treatment process of the waste etching liquid is executed.