PURPOSE: To perform purification of water efficiently with little energy consumption by arranging two rotary disk bodies provided vertically and in parallel to each other to a main shaft so as to direct the directions of both main shafts of the rotary disks in parallel to each other and in the longitudinal direction of a water tank, and arranging the degree of immersion of both disks to ca. 40%.

CONSTITUTION: Two rows of belt conveyor are formed on each stage of a water tank 4 partitioned to two stages and contg. rotary disks in the longitudinal direction of the water tank 4 by installing belts 15 to plural numbers of idle roller 8 and rotary roller 11 arranged in the longitudinal direction of the water tank 4. Further, many plate blades 16 comprising flat plates or bent plates are disposed to bestride the two belts 15 so as to be driven by a driving motor 14 and a driving chain 13. In this way, a belt conveyor type stirring mechanism is provided to the bottom of each stage of the water tank 4 contg. disks. The stirring mechanism is driven in the direction vertical to the direction of rotation of the disks with nearly the same rotational speed as the peripheral speed of the rotary disks at the stage of driving of the rotary disk bodies 5a, 5b.