To provide a method which enables drainage treatment at a low cost as a result by carrying out granulation of a microbe efficiently in a short time to maximally exhibit an advantage of the microbe treatment using a granule.

The method for treating the drainage comprises bringing the drainage into contact with it together with the microbe in a container charged with a powder having a diameter of 0.5 mm or smaller, and specific gravity of 1.0 or larger and 7.0 or smaller.