An auto distinction system images an assembled fiber band which continuously moves on the front side of a background plate applies sync-separating to a video signal by a sync-separating circuit 5a, and clamps the video signal by a clamping circuit 5b. Based on the clamped image signal, the characteristic information containing the defect information of the assembled fiber band is detected, and the defect information is extracted from the detected characteristic information. The clamped image signal is supplied to a noise-eliminating circuit 6a and a defect signal concerning the thickness of the assembled fiber band is extracted. Based on the extracted signal and a reference signal with respect to the information, suitability of the defect information is discriminated by a distinction circuit 7. When the results of distinction are defective, the results are announced. The characteristic information can be used for process control by being supplied to an external computer.