A paper processing device includes a casing, a transfer roller assembly and a paper pressing mechanism. The casing includes a paper placement platform. The plural papers from a printing device are transferred to the paper placement platform by the transfer roller assembly. The paper pressing mechanism is located under the casing. The paper pressing mechanism includes a support frame, a pressing bar, a driving mechanism and a linking mechanism. The pressing bar includes a protrusion block. The protrusion block is penetrated through an opening of the casing. The protrusion block and the paper placement platform face each other. The linking mechanism is connected between the driving mechanism and the pressing bar. While the linking mechanism is driven by the driving mechanism, the pressing bar is moved linearly relative to the support frame, and the protrusion block is moved from an initial position to a target position.