To provide a method for recycling washing water used when a film having a carbon particle-based backing layer is treated, particularly when the carbon particle-based backing layer is removed and washed.

The discolored washing water is recycled in high efficiency by making washing water pass through the ultrafiltration equipment in which an electrified hydrophilic ultrafiltration membrane, for example, an acrylonitrile copolymer-based membrane is set so that the water consumption in this step to treat the film can be saved remarkably.