PURPOSE: To distinguish the flaw, soiling, deformation and other defects of the surface of dry cells or the like and sort good products from defective products, without accurately matching with the specified dimensions, by comparing two signals obtained at adjacent parts on the object being inspected in a comparator circuit.

CONSTITUTION: The object being inspected 6 is placed on a rotary table 7, opposite to a camera 1, and is illuminated by a illumination 5 such as a circle-lined fluorescent lamp or the like. The reflected light is introduced into the camera 1. The beams of light reflected from parts (a), (b), and (c) of the object 6 are successively admitted into the camera 1, and the outputs thereof are temporarily stored in a shift register circuit 11 and are at the same time sent into a comparator circuit 12. This comparator circuit 12 compares the signal on the straight line (a) from the register 11 with the signal on the straight line (b) from the camera 1, and, when a difference beyond a specified value is found, emits a defect detecting signal. In consequence, the output on the straight line (b) is compared with that on the straight line (c), and the observation on the entire surface is terminated when the rotary table 7 makes a 180-degree turn