Provided is a banknote processing device that can efficiently perform a deposit process with respect to a large quantity of banknotes. The banknote processing device is provided with: a deposit aperture through which banknotes are introduced; a conveyance unit that conveys the banknotes of the deposit aperture; a deposit aperture opening/closing member that can open/close the deposit aperture by means of moving; and a control unit that controls the conveyance of banknotes by the conveyance unit and the opening/closing operation of the deposit aperture opening/closing member. When a halting event of a calculating process has arisen during the calculating process of banknotes introduced to the deposit aperture, the control unit temporarily halts the calculating process and opens the deposit aperture opening/closing member.