Sewage treatment is carried out at high performance from a treatment at high load to a treatment at low load at all times, irrespective of seasonal change and region where sewage treatment equipment is installed, and no excess sludge is discharged outside the equipment at all. Whirl water flow generating means and a heating pipe are disposed in sewage treatment tanks in which a number of activated sludge process beds and aeration pipes are disposed. A sewage water under treatment is returned from a third sewage treatment tank, to first and second treatment tanks, for example. A sedimentation tank and a sludge digestion tank are also disposed so as to supply the supernatant obtained after the sludge treatment to the first sewage treatment.