A bill processing device, comprising a unit for storing and retrieving bills (2) positioned on the inner upper side of a casing, a base unit (3) positioned on the inner lower side, and one to multiple stages of intermediate units (4A) to (4C) positioned therebetween, the unit for storing and retrieving bills (2) further comprising a bill leading-in mechanism (21), a bill leading-out mechanism (23), and a transfer mechanism (29), the base unit (3) further comprising a bill storage part (31), a transfer mechanism (32), and a taking-in and delivering mechanism (34), the intermediate units (4A) to (4C) each further comprising a bill storage part (41), a transfer mechanism (42), a taking-in and delivering mechanism (44), and a bill moving direction switching means, whereby the elements forming the bill storage parts and transfer mechanisms are formed commonly to each other, the extension and reduction of the bill storage parts can be performed easily by a necessary and minimum change, and bills can be stored into and retrieved from each storage part.