To provide a serial number recognition device having a sufficiently improved recognition rate that shows a ratio of the number of paper sheets whose serial numbers are recognized to all paper sheets to be processed.

An image processing part 34 reads a character image in a first serial number area and a character image in a second serial number area, for a character of a digit to be processed (s32), and generates a logical sum image of them (s33). When there are a plurality of dot pieces in the logical sum image created in s33 (s34), the image processing part 34 detects a circumference length of each dot piece (s35). The image processing part 34 extracts the dot piece having the maximum circumference length, as the target character (s36). The image processing part 34 recognizes the character related to the dot piece generated in s36, and sets the character recognized as the character of the target digit (s37). When there remains an unprocessed digit (s38), the image processing part 34 returns to s31, and repeats the processing.

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