Disclosed herein is a spin drier for silicon wafers and the like including a rotor equipped with at least one holder for a carrier, which is adapted to enclose a silicon wafer or the like therein, and a casing embracing the rotor. The radial distance between the circumferential wall of the casing and the central axis of the rotor gradually increases as the circumferential wall extends all around the rotor in its circumferential direction from a position adjacent to an air exhaust port to the air exhaust port, thereby making an air conduit formed around the rotor gradually wider. The bottom wall of the casing gradually slopes down towards the air exhaust port. Owing to the above construction, the resistance to an air stream through the casing has been reduced, thereby preventing air from flowing back into the rotor after striking the circumferential wall of the casing and thus preventing stains and water on the circumferential wall of the casing from flowing back and sticking on wafers or the like.