PURPOSE: To detect delicate linear defects and planar defects such as color irregularities accurately by integrating and differentiating image signals in the scanning direction and the orthogonal direction with respect to the scanning line at the same time with an image sensing device such as TV camera.

CONSTITUTION: When the video image signals detected with an image sensing device are dot-shaped image signals P, integration is performed in the direction of the scanning line with a first integrating device 6 (figure b). The value is smoothed and continuously differentiated in a differentiating device 9. As a result, the clear change in signal is obtained at the same position as shown in the figure (d). Meanwhile, integration is performed in the vertical direction with respect to the direction of the scanning line in a second integrating device 7 (figure e). The value is smoothed and continuously differentiated in the differentiating device 9. As a result, the clear change in signal can be obtained at the same position as shown in the figure (g). The figures (d) and (g) are compared in a defect judging device 10, and the dot-shaped defect in the surface is judged.