To surely prevent drying failure without any increase in drier size, in regard to the drier in which water content of supplied material to be treated varies.

An ash drier 1 is mainly composed of a feeder 3 for transporting wet ash; a drier 2 driven by an electric motor 27 for the drier to dry the wet ash supplied from the feeder 3 and discharge the same; and a control device 9 for controlling the operation of the drier 2 and the feeder 3. The control device 9 includes: a current value sensor 93 for detecting a current value of the electric motor 27 for the drier; and a feed regulating part 61 for acquiring a detected current value detected by the current value sensor 93 and regulating the feed of wet ash from the feeder 3 to the drier 2 according to the detected current value.