Abstract: According to the invention, a device for detecting counterfeit paper currency is provided which utilizes the characteristic fluorescence of genuine paper currency to detect counterfeit paper currency. An ultraviolet lamp illuminates the paper currency of unknown origin which the currency is placed on a stage held in fixed relationship to the ultraviolet lamp by a housing. A sensor circuit responds to the fluorescent radiation from the paper currency to give a signal to an indicator which displays an indication of the fluorescence of the unknown paper currency relative to genuine paper currency. The sensor is a photoresistor and the indicator is a variable intensity light or a digital display.