To provide a treating device for sewage which cleans much sewage discharged from various factories, various facilities and living environments.

Sewage is sent to a fist treating tank 5, and filth in sewage is caught by gas generated at a fist electrode part 6 and floats up to the surface layer as foam K and is scooped out and recovered by a fist recovery means 13. Fine particles floating in sewage are mutually coupled into coarse particles in a reaction tank 9 and are returned to a mixing tank 3 and are mixed with raw water and are sent to the first treating tank 5 again and are deposited as gross particles in the first electrode part 6. Gross particles deposited in the first treating tank 5 are sent to a flocculation auxiliary injection tank 21 and are further sent to a second treating tank 25 and is caught by gas generated by a second electrode part 26 and floats up as foam K and is scooped out by a second recovery means 30.