PURPOSE: To efficiently recover the low concn. substance in washing water, by treating washing water by a medium pressure reverse osmosis membrane apparatus while treating the concentrate therefrom with a high pressure reverse osmosis membrane apparatus and applying electrolytic treatment to the concentrate to recover the contained substance.

CONSTITUTION: Washing water A used in photographic treatment passes a pretreating part while the treated water is sent to a medium pressure reverse osmosis membrane apparatus 1 where receives primary separation treatment to be separated into permeated water B and a concentrate A1. The permeated water B is re-utilized as washing water or discharged while the concentrate A1 is supplied to a high pressure reverse osmosis membrane apparatus 2 where subjected to secondary separation treatment to be separated into permeated water B1 and a concentrate A2. The permeated water B1 is re-utilized as washing water or discharged while the concentrate A2 is subsequently treated with an electrolytic apparatus to recover silver. In this case, 10g/l of high purity silver is recovered from the concentrate A2. Waste water B2 from the electrolytic apparatus 3 after silver recovery is discharged after subjected to ozone treatment.