PURPOSE:To make it possible to remove foreign materials in raw cotton with a high accuracy, by opening the raw cotton, observing the opened raw cotton with a color sensor, etc. while conveying the raw cotton with an air stream and separating the foreign materials. CONSTITUTION:Raw cotton is carried on an air stream, received from an inlet duct (3a) in a fiber collecting part 9 and separated from the air stream. The raw cotton is fed to a conveying part 10 and the air stream is fed to a duct (3c), opened by delivery rollers 26 and an opening roller 28 in the conveying part 10, passed through a rising air conveying duct 11, conveying duct (3f) and air supply device 5 by an air stream and delivered from a delivery duct (3b). An observation window 31 for discriminating colored matter (foreign material) mixed in the raw cotton is provided in the course of the rising air conveying duct 11.
