PURPOSE: To detect the defective part stabely and highly accurately even if there is unevenness in illuminance at the inner surface of a container by setting an objective region for inspection for the part between the initial rise-up point and the last falling- point of every scan on the image signal, which is obtained by binaray-coding the multivalued variable-desntity image signal with a threshold level.

CONSTITUTION: A region detecting circuit 21 binary-codes a multivalued variable-density image signal 1a from a frame memory 1 through a window-gate circuit 5E with an outer-shape binary-coding threshold value THG. The first rise-up point 61 of the signal and the last fall-down point 62 are detected. A region signal 21a, wherein the part between the points 61 and 62 is the processing range, is outputted. The AND conditions of the signal 21a and the variable-dinsity image signal 22a for one scanning line corresponding to the signal 21a are gated 23. A variable-dinsity image signal 23a in an object region is outputted. The defective picture elements including the defective peak and bottom are detected 24. The element and the result of the circular inspection of a high-luminance-part judging circuit are judged with a synthetic judging part 15. The good or bad state is outputted from an output circuit 16 based on the output judgment signal.