A diagnostic apparatus in an image recognition system able to quickly and accurately detect breakage of a cable from an image sensor or pixel burn of an image sensor, provided with a histogram computing unit for performing predetermined computations on an image signal fetched into an image recognition unit to generate a density histogram and an abnormality judging unit for analyzing the density histogram generated by the histogram computing unit to judge the presence of an abnormality or alternatively provided with a memory unit for receiving as input and storing information of an image signal fetched into an image recognition unit and a comparing/judging unit for reading out and comparing information of image signals of a plurality of images different in time relating to a target pixel from the memory unit and judging whether they are the same or different and judging that there is an abnormality when they are the same.