PURPOSE: To increase the capacity for treating sanitary sewage by dehydrating the sanitary sewage, releasing the separated water to an arbitrary place and housing only the dehydrated cake into a tank.

CONSTITUTION: The sanitary sewage is sucked into a sanitary sewage chamber 8 of the storage tank 2, then the sanitary sewage is supplied to a dehydrating cage 13 of a centrifugal separator 3, where the sanitary sewage is dehydrated and is separated to caky solid and separated liquid. The separated liquid is released to the arbitrary place and the caky solid is scraped from the inside peripheral face of the dehydrating cage 13 by a suction pipe 15 and is sucked by a suction pipe 17 so as to be housed into the dehydrated cake chamber 9 of the storage tank 2. The pressure in the sanitary sewage chamber 8 is reduced and intensified by a rotary blower 4 and the pressure in the dehydrated cake chamber 9 of the tank 2 is reduced. As a result, the capacity for treating the sanitary sewage is increased.