PURPOSE: To surely prevent illegal using action, such as a beltlike foreign matter adhered to a bank note even when the bank note is true, and illegal use action of a false bank note and to prevent the occurrence of a cause for a trouble, such as the stop of the function of a discriminating device, occurring owing to insertion of a paper sheet having an off-specification size compared with a regular paper sheet, such as a used telephone card and a commutation ticket the term of which expires.

CONSTITUTION: In a paper discriminating device, a discriminating element 8 is arranged in the rear of a paper sensing sensor 5 located in the, vicinity of a paper insertion slot 4 and a conveyance belt 6 is arranged in the vicinity thereof. A shield shutter 7 to block entrance of an illegal paper throughout a whole width is arranged between the paper sensing sensor 5, the discriminating element 8, and the conveyance belt 6.