To reduce device cost and operating cost by efficiently drying hydrous waste such as highly-hydrous waste.

A drying system of the hydrous waste comprises a storage tank for storing the hydrous waste, a superheated steam generator for generating superheated steam, and an external heating type stirring dryer for stirring/drying the hydrous waste while making the hydrous waste supplied from the storage tank directly contact with the superheated steam supplied from the superheated steam generator. The drying system of the hydrous waste comprises a circulation route for returning the steam exhausted by the external heating type stirring dryer to the external heating type stirring dryer, and an exhaust part for exhausting surplus steam from the circulation route. The circulating steam is heated by a superheater while introducing waste heat from an incinerator of sewage gas accompanied by sludge treatment, an incinerator of the sludge, or a treatment furnace.