PURPOSE: To find an abnormality of winding in the early stage, to eliminate the omission of check and to reduce the labor of a worker by detecting the abnormality of winding of the inside diameter of a coil when the number of state changes of darkness/ brightness information of every picture element, which is caused by movement of a carried coil, in the coil carrying direction is larger than a set value.

CONSTITUTION: A coil 10 carried on a coil carrying line 14 is placed vertically to the line advance direction, and only a one-dimensional darkness/brightness signal on one straight line is gathered by a one-dimensional image sensor 30 which the surface of the outside diameter of the coil faces vertically. This darkness/brightness information is amplified and is inputted to an input device 40A as a binary signal (1, 0), and it is reset for every one pulse of a pulse generator 36, and darkness/brightness information indicating the next shape due to coil movement information is gathered, and this operation is repeated, and information is stored and processed to obtain one-picture components of information. An operation processing device 40 scans one-picture components of stored picture elements to totalize the number of state changes (0→1) and (1→0), and the abnormality of the inside diameter is discriminated if this number is larger than, for example, 6.