The precision of detection of abnormal media is increased using a unique identification number. A banknote deposit/withdrawal mechanism of an automated teller machine confirms whether a banknote having the same serial number is among transaction banknotes by comparing each transaction serial number obtained by reading the serial number for each transaction banknote with other transaction serial numbers. Thereby, when counterfeit notes having the same serial number are included among the transaction banknotes, the banknote deposit/withdrawal mechanism cannot determine a banknote as counterfeit in a process of collating the serial numbers with a counterfeit note serial number list, but can determine that a banknote is counterfeit in a collation process between the transaction serial numbers. In this case, the banknote deposit/withdrawal mechanism can prevent counterfeit notes from being transferred to a user by transporting a relevant transaction banknote together with all other transaction banknotes to a reject compartment.