The present invention provides a medium processing device and a medium transaction device with which stability is increased by shortening the transport path. In other words, a paper currency deposit/withdrawal device has a transport section that forms a linear transport path along the front/back direction within an upper block, near the boundary between the upper block and a lower block, and an upper storage compartment is arranged near the back end in a rear transport section, with counterfeit notes being transported to the upper storage compartment by means of a switching unit. Thus, by minimizing the length of the transport path in this paper currency deposit/withdrawal device, it is possible to reduce the frequency with which malfunctions such as paper currency jams occur, and it is possible to prevent the distribution of counterfeit notes, by distinguishing and storing such notes separately from legitimate paper currency, reject paper currency, and the like.