A post-processing device includes a cylindrical body and branching guides. The cylindrical body is rotatable. The cylindrical body and the branching guides convey paper to a processing unit that processes the paper and to an ejection tray. A paper reversing mechanism is composed mainly of the cylindrical body and the branching guide, in which a first face of the paper is directed to a peripheral surface of the cylindrical body and the paper is wound therearound by rotating the cylindrical body. The paper reversing mechanism then rotates the cylindrical body in a reverse direction and switches the posture of the branching guide, to thereby separate the paper from the peripheral surface and eject.