To obtain an efficient water purifying magnetic separator separating a substance to be separated from washing water to concentrate the same without providing a magnetic field generating means separately from a water purifying magnetic separation part.

Raw water in a reservoir 1 is once stored in a raw water tank 5 through a filter 3 and a magnetic powder is added herein to guide the raw water to a water purifying magnetic separation container 15a as magnetic floc. A magnetic separation part is equipped with the container 15a being a first magnetic container, an air-core coil 16, a high grade magnetic filter 20a being a first magnetic filter, a perforated magnetic pole 18a and a yoke 19. A small concn. magnetic separation container 15b is provided as a second magnetic container and a filter 20b and a perforated pole 18b are built in the container 15b in the same way. Pretreated water 12 is filtered by the filter 20a in the first magnetic container 15a to attract magnetic floc to purify raw water and, after the filter 20a is backwashed, backwashing waste water containing the magnetic floc is filtered by the second filter 20b to attract the magnetic floc and the treated water is allowed to flow to the second filter 20b and concn. waste water high in the concn. of magnetic floc is obtained from backwashing waste water.