A medium transaction device includes: a conveyance section for a medium; a customer interface attachment point; a classification section attachment point; a storage section attachment point; and a controller that controls transaction processing of the medium with the user. At least one of the customer interface attachment point, the classification section attachment point, or the storage section attachment point is configured to allow attachment of one type of the customer interface, the classification section, or the storage section from plural mutually different respective functional types thereof. The controller switches the transaction processing executable with the user according to the type of the customer interface, the classification section, or the storage section that is attached to the customer interface attachment point, the classification section attachment point, or the storage section attachment point.