A banknote handling apparatus for recognizing and handling banknotes, the apparatus comprising: a depositing unit configured to deposit the banknotes; a dispensing unit configured to dispense the banknotes; a plurality of banknote storing units configured to store the banknotes; a transport unit configured to transport the banknotes; a recognition unit provided at the transport unit, and configured to recognize the banknotes; a control unit configured to control the handling of the banknotes; and a chamber for an optional attachment to which a cassette attachable to and detachable from the banknote handling apparatus with the banknotes stored, or an additional storing unit provided in addition to the banknote storing units is selectively attachable; characterized in that: the control unit includes an option control unit performing control corresponding to an attached state of the cassette or the additional storing unit, and control corresponding to an unattached state, the option control unit has common firmware corresponding to the attached state of the cassette, the attached state of the additional storing unit, and the unattached state, and the firmware is switchable among a mode of performing the control corresponding to the attached state of the cassette, a mode of performing the control corresponding to the attached state of the additional storing unit, and a mode of performing the control corresponding to the unattached state of the cassette and the additional storing unit, and when the cassette or the additional storing unit is attached, the control corresponding to the unattached state is performed by switching the firmware to the mode of performing the control corresponding to the unattached state. a depositing unit configured to deposit the banknotes; a dispensing unit configured to dispense the banknotes; a plurality of banknote storing units configured to store the banknotes; a transport unit configured to transport the banknotes; a recognition unit provided at the transport unit, and configured to recognize the banknotes; a control unit configured to control the handling of the banknotes; and a chamber for an optional attachment to which a cassette attachable to and detachable from the banknote handling apparatus with the banknotes stored, or an additional storing unit provided in addition to the banknote storing units is selectively attachable; characterized in that: the control unit includes an option control unit performing control corresponding to an attached state of the cassette or the additional storing unit, and control corresponding to an unattached state, the option control unit has common firmware corresponding to the attached state of the cassette, the attached state of the additional storing unit, and the unattached state, and the firmware is switchable among a mode of performing the control corresponding to the attached state of the cassette, a mode of performing the control corresponding to the attached state of the additional storing unit, and a mode of performing the control corresponding to the unattached state of the cassette and the additional storing unit, and the control unit includes an option control unit performing control corresponding to an attached state of the cassette or the additional storing unit, and control corresponding to an unattached state, the option control unit has common firmware corresponding to the attached state of the cassette, the attached state of the additional storing unit, and the unattached state, and the firmware is switchable among a mode of performing the control corresponding to the attached state of the cassette, a mode of performing the control corresponding to the attached state of the additional storing unit, and a mode of performing the control corresponding to the unattached state of the cassette and the additional storing unit, and a mode of performing the control corresponding to the attached state of the cassette, a mode of performing the control corresponding to the attached state of the additional storing unit, and a mode of performing the control corresponding to the unattached state of the cassette and the additional storing unit, and when the cassette or the additional storing unit is attached, the control corresponding to the unattached state is performed by switching the firmware to the mode of performing the control corresponding to the unattached state.