PURPOSE: To form a dry powdery material, especially a photographic org. compd., by supplying a soln. to be dried held at a specified viscosity into a long steam-heating pipe and injecting a mixture of the dried powder generated in the heating pipe and a gas in a reduced-pressure atmosphere.

CONSTITUTION: The soln. to be dried (e.g. a polymer having a photographic useful group) controlled to 1-50 centipoise in a diluted soln. tank 1 is quantitatively supplied into the long steam-heating pipe 3 through which pressurized steam is passed. The mixture of the dry powder generated in the heating pipe 3 and a gas is injected into a vacuum vessel 4 in the reduced-pressure atmosphere, and separated into the dry powder and the gas. As a result, the photographic org. compd., especially a polymer having a photographic useful group, is separated from the soln., and many kinds of products can be obtained easily and inexpensively by a single device.