PURPOSE: To prevent an incorrect judgment without generating an abnormal waveform as long as a woven cloth is normal even when an illuminating environment is changed by a method wherein an image signal in which a waveform component inherent in a normal woven cloth has been removed from an image signal obtained as an imaged result is compared with a tolerance.

CONSTITUTION: A CCD camera 4A detects a flaw and a small dotlike flaw in the weft direction of a woven cloth 1, and the whole width of the woven cloth 1 is covered by three cameras. A CCD camera 4B is used to detect a large flaw such as a stain, a spot or the like, and the whole width of the woven cloth 1 is covered by two cameras. A CCD camera 4c is used to detect a flaw in the warp direction, and the whole width of the woven cloth 1 is covered by three cameras. Then, in a signal processing system 13, an image signal in which a waveform component inherent in a normal wove cloth has been removed from an image signal obtained as an imaged result is compared with a threshold value by a digital comparator so as to judge an abnormality, and the abnormality is taken into an image memory so as to be output to the outside.