PURPOSE: To extract a maximum or minimum value from plural image data without sorting them.

CONSTITUTION: This device is provided with N stages of examining circuits 100-400 corresponding to the respective bits of N-bit image data. The examining circuit of an (i)th stage (i is 1 to N) finds new examination signals XP2-XT2 showing which of M (5) image data is candidate data on the basis of the value of the (i)th bit of each image data from the most significant digit bit as to image data specified as candidate data with examination signals XP3-XT3 supplied from the precedent stage. Thus, examination signals are found in order for every stage and the maximum value or minimum value is specified with the examination signals XP-XT obtained by the examining circuit 400 of the lowermost stage.