A medium processing device includes holding section that temporarily retains a medium therein. A gear inside the holding section drives a mechanism that stores the medium into and feeds out from the holding section. A main body includes a mounting location at which the holding section is mounted, and transfers the medium to and from the holding section at a time at which the holding section is mounted. An operation knob transmits, to the gear, a rotary operation applied from outside the holding section. An operation restriction portion at the main body, blocks transmission of the rotary operation from the knob to the gear in a mounted state in which the holding section is mounted at the mounting location, and allows transmission of the rotary operation from the knob to the gear in a detached state in which the holding section is detached.