PURPOSE: To improve the maintenance of the titled device by simplifying the device so as to allow a supply of sewage to be made continuously by a method wherein the sewage is taken out from a sewage pit directly through a hose and is mixed with powdered coal.

CONSTITUTION: The sewage 12 is sucked up by a vacuum pump 25 connected to a hose 24 inserted into the sewage pit 6 and th powdered coal is sucked by a powdered coal hopper 7. The powdered coal and the sewage 12 are mixed and kneaded by a screw 24 provided near the inlet port of the vacuum pump 25 and the amount of the mixture is measured by a sewage amount measuring device 16 provided at the outlet port of the vacuum chamber. Further, the number of revolutions of the vacuum pump 25 is controlled by the sewage supply control device 17 so as to meet the incinerating capacity of the fluidized bed furnace 1 to thereby control the amount of the kneaded sewage. The control of the amount of powdered coal is made by adjusting the opening degree of a powdered coal adjusting valve 23. As a consequence, the sewage supply control device is simplified and the supply of the sewage is controlled continuously to thereby facilitate the maintenance of the device.