To extremely prevent the generation of powder dust compared with this kind of a conventional drying device, to provide a flow passage with structure to be decreased in an influence exercised on a drop port for a substance to be dried without narrowing a flow passage for hot gas, and to increase the size of the whole of the device through planer enlargement without increasing only height.

This drying device is divided into a first chamber having a drying surface 7A; a second chamber having a drying surface 7B; a third chamber having a drying surface 7C; and a fourth chamber having a drying surface 7D. A step being low in a head between present and subsequent drying surfaces and a substance to be dried drop to a subsequent surface are formed at and in the drying surface 7A or 7D. Chambers are disposed in a helical stair-form state from a topmost step to a lowermost step through intercoupling the adjoining steps, and constitution is performed such that the substance to be dried is dropped, in order, from the topmost step to the lowermost step through a step low in a head. Further, the flow passage cross section of an opening part for a hot gas flow passage is enlarged as much as possible.