In a fluidized bed type gasification furnace 1 for thermally decomposing wastes, a temperature of a fluidized bed 1a is maintained within a preferable range, even if the wastes containing a dewatered sludge having higher water content than the conventional wastes is processed. A waste treatment facility 100 is constructed in vicinity of a cement production facility 200. The apparatus comprises the fluidized bed type gasification furnace 1 for gasifying the wastes to generate a pyrolysis gas, and a gas transport line 6 for transporting the generated pyrolysis gas with entrained char and ash to a preheater 10 or a calciner 20 for cement. The apparatus also comprises a temperature elevating device such as a gas air heater 41 and the like, which elevates the temperature of the estimated value that is supplied to the gasification furnace 1 by utilizing waste heat of the cement production facility 200