To prevent illegal medium usage by a criminal in a medium processing device which is to be equipped on devices and equipment, such as, mainly an ATM and a CD.

Medium information recorded in a medium 21 is controlled to be stored and held in a memory by being read via a medium information reading means 6, while the medium 21 is transported into an inserting direction by transport means 7, 8. Whether the medium 21 can be ejected is determined, by transporting the medium 21 into an eject direction by the transport means 7, 8. The medium information held in the memory is controlled to be ejected, when it is determined that the medium 21 can be ejected. As a result, the medium information recorded in the medium 21 cannot be outputted to an upper-level device, unless it is confirmed that the medium 21 can be ejected. Thus, unauthorized use of the medium 21 by the criminal can be prevented, by avoiding the situation where a password is subjected to sneak look by someone else.