PURPOSE: To continuously perform the filtering of various sewages such as raw sewage or the like at high speed for a long time by providing a bed packed with small porous bodies having elasticity in a tank and arranging sewage supply parts over many stages in the height direction of the packed bed.

CONSTITUTION: A bed 3 packed with small porous bodies having elasticity is provided in a treatment tank 2 and sewage supply parts 10-12 are arranged over many stages in the height direction of the packed bed 3 and sewage is distributed and supplied to take out filtered treated water from the treated water outflow pipe 4 provided to the lower part of the packed bed 3. As a result, various sewages such as raw sewage or the like can be continuously filtered at high speed for a long time.