To provide a sewage sludge treatment method and its device capable of burning sewage sludge, collecting the incinerated ash in a combustion exhaust gas by a dust collector, and stably solidifying the incinerated ash with simple operation to make a solid material of high strength.

The sewage sludge and calcium-containing substance are supplied to a fluidized bed furnace kept at high temperatures of about 800-950°C to burn the sewage sludge, then high-temperature combustion exhaust gas is cooled, the incinerated ash existing in the exhaust gas is collected by the dust collector, and the water is added to the collected incinerated ash to granulate/solidify the incinerated ash. Further the amount of the calcium-containing substance supplied to the fluidized bed furnace is controlled to adjust a ratio MC/(MS+MA) of the amount MC(mol) of a calcium component in the calcium-containing substance supplied to the fluidized bed furnace and MS+MA obtained by adding the amount MS(mol) of a silicon component in the sewage sludge and the amount MA(mol) of an aluminum component in the sewage sludge to be 0.1 2.