To provide a drying treatment system or the like by which a treatment apparatus for organic sludge can be downsized by enhancing the evaporation efficiency of moisture comprised in the organic sludge and the drying speed of the organic sludge, and condensed water can efficiently be treated.

The drying treatment system 1 for organic sludge comprises: an organic sludge drying apparatus 4 with an exhaust gas G1 of ≤450°C exhausted from a waste incinerator 2 as a heat source for drying organic sludge SL; a water vapor condensing apparatus 8 condensing water vapor generated by drying by the organic sludge drying apparatus 4; and an incineration ash water-cooled water-washing apparatus 10 utilizing water W condensed by the water vapor condensing apparatus 8 for the water-washing of the incineration ash A. The system is preferably provided with a decomposition substance adding apparatus 7 adding a substance decomposing protein in the organic sludge SL at the inside of the organic sludge drying apparatus 4 or at the prestage thereof.