Abstract: In a bill examination device in which a signal pattern obtained by scanning the bill with a photo-detector or a magnetic detector is compared with a reference for testing the authenticity, the signal is subjected to differentiation or removal of a direct-current component before the comparison. The effect of the differences or offsets of the detector or its associated circuit due to manufacturing variations, temperature change, or aging, and differences in the darkness of printing or smudge on the bill is reduced, and the reliability of the authenticity test is improved.