Abstract: The present invention relates to a detector (1) of foreign fibres and to a corresponding detection method, which can be used for detecting foreign fibres and foreign materials in a measurement object (5) in the textile industry, for example in yarns, slithers and unformed fiber bands on, for example, weaving machines, spinning machines, bobbin winding machines, doubling machines, cards, drawing benches and bobbin frames . . . . The principle of the detection is based on the fact that a measurement object (5) and foreign fibres or materials which are situated in the measurement object (5) absorb the light emitted into the measurement volume (4) by a light source (2) to different extents. All the light in the measurement volume (4), or a representative sample thereof, is measured by photodetectors (3) and converted into a photoelectric signal.