To surely distinguish multiplex bank notes in a simple structure.

A sensing station 12 is included, which is arranged so as to detect light from a light emitter 48 permeating an object comprising a single sheet or multiplex sheet making a supply route communicate to be provided in the sensing station 12 to have the light emitter 48 and an optical sensor 50. In the optical sensor 50, output voltage changing its intensity by intensity of permeating light received by the optical sensor 50 is supplied. This output is supplied to a first input 58 of a log ratio amplifier 60. In the case of not providing the object in the sensing station 12, voltage representing an output of the optical sensor 50 is supplied to a second input of an amplifier 64. An output of the amplifier 60 is supplied to a data processing means 52, whether a single or multiplex sheet of the object is provided or not in the sensing station 12 is judged in the data processing means.