PURPOSE: To surely inspect vegetables which have been stained or whose color and shape are different by a method wherein the vegetables are held on a holding part covered with a material which easily absorbs infrared rays, the vegetables are irradiated with infrared rays, their reflected light is received, the image of the holding part and that of the vegetables are constituted, the images are converted into digital signals and the signals are processed.

CONSTITUTION: Vegetables 14 are placed on a holding part 12 which is composed of a conveyance stand or the like in such a way that their contour does not protrude to the outside of the contour of the conveyance stand 12, infrared rays are radiated from infrared illumination devices 16, beams of their reflected light are received by a CCD camera 18, A/D-converted 22 and then sent to a CPU 26. Since the conveyance stand 12 is constituted of a rubber or the like, its reflection factor is low, the vegetables 14 which contain chlorophyll reflect the infrared rays at a definite high reflection factor, and image signals can be binary-coded easily. The CPU 26 stores the input image of the conveyance stand 12 and that of the vegetables 14 into a memory 24a as multivalued images at every pixel, the conveyance stand 12 and the vegetables 14 are divided by a threshold value stored in a memory 24b, the size of the vegetables 14 is detected on the basis of criterion data stored in a memory 24, the quality of the vegetables is judged, and the vegetables are sorted.