To provide a method of treating sewage with high efficiency by aeration using a microorganism activator.

In sludge treatment equipment having plural sludge separation tanks, a water passing vessel 4 in which a durable granular microorganism activator 3 is housed is thrown in sewage in a preceding aeration treatment tank 2, hung in mid-liquid, and also together with it, a quick-acting powdery microorganism activator 5 is thrown in, and sewage in the preceding aeration treatment tank 2 is aerated to air mixed with a little pure oxygen 1 to propagate aerobic microorganisms in large quantities, by which the formation of flocs is promoted. In a succeeding aeration tank 6, normal aeration by air is performed, and precipitated sludge 14 generated in a final sludge separation tank 1 is returned to the preceding aeration treatment tank 2 or an air current quantity adjusting tank 8 upstream thereof in which normal aerastion is performed.