Device and method for verifying the authenticity of banknotes

An apparatus and method for testing the authenticity of bank notes are proposed. The apparatus includes a light source for emitting light suitable for exciting fluorescent light in a bank note to be checked, and a fluorescence detector for detecting the fluorescent light emitted by the bank note to be checked. According to the invention it is provided that the light source is a light-emitting diode and the light-emitting diode is formed to emit light containing ultraviolet light at least in a partial spectral region. This makes it possible in particular to obtain a compact structure of the apparatus. The method involves exciting and detecting fluorescent light in the bank note to be checked and comparing the detected fluorescent light with a predefined threshold value. According to the invention it is provided that the detected fluorescent light is reduced by the ambient light detected with the light source switched off. This permits the elimination of measuring inaccuracies at the same time as simple operation.