FLUORESCENT THREAD DETECTING DEVICE

PROBLEM TO BE SOLVED: To provide a fluorescent thread detecting device which can extract a fluorescent thread with simple constitution. SOLUTION: The fluorescent thread detecting device 8 has a housing 9, which contains an ultraviolet-ray LED 11 irradiating a paper money 2 with ultraviolet rays. In the housing 9, a photodiode 14 which receives fluorescent light excited by the fluorescent thread S by the irradiation with the ultraviolet rays and a photodiode 17 which receives reflected light of the ultraviolet rays are stored. The output signals of those photodiodes 14 and 17 are amplified by operational amplifiers 19 and 20 respectively and inputted to an operational amplifier 21, which amplifies the difference between the output signals of the operational amplifiers 19 and 20. Consequently, only components of the fluorescent thread S are sharply extracted.