An apparatus for detecting foreign substances in a fiber tuft stream and for separating the foreign substances therefrom, includes a conduit guiding the fiber tuft stream therethrough in a conveying direction; a metal detector situated at a first location of the conduit for detecting a metal substance in flight and for emitting signals representing the metal substance; a first separating device situated at a second location of the conduit downstream of the first location as viewed in the conveying direction; a first control device connected to the metal detector and the first separating device for operating the first separating device in response to a signal emitted by the metal detector for removing the detected metal substance; an optical sensor situated at a third location of the conduit for detecting a non-metal substance in flight and for emitting signals representing the non-metal substance; a second separating device situated at a fourth location of the conduit; a second control device connected to the optical sensor and the second separating device for operating the second separating device in response to a signal emitted by the optical sensor for removing the detected non-metal substance.