A medium processing device includes a processing unit performing processing on a medium, a processing tray on which the medium is placed, a discharge roller pair configured to discharge the medium, a feeding unit configured to feed the medium to the processing tray and the discharge roller pair, and a curvature applying unit configured to apply curvature to the medium along a width direction intersecting a conveyance direction. The discharge roller pair includes a first roller and a second roller. The second roller is displaceable between a first state where the second roller can nip the medium with the first roller, and a second state where the second roller is more separated from the first roller. The curvature applying unit is in a curvature applying state when the second roller is in the second state, and in a retracted state when the second roller is in the first state.