A post-processing apparatus comprising: a conveyor (10 to 19) configured to convey recording media on each of which an image is formed by an image forming apparatus; a tray configured to hold the recording media conveyed by the conveyor (10 to 19); a binder including a cartridge containing a plurality of staples, the binder being configured to bind the recording media on the tray with the plurality of staples in the cartridge; and a binder mover configured to move the binder in a main scanning direction that is orthogonal to a conveyance direction of the recording media conveyed by the conveyor (10 to 19), the binder mover including: a motor; the post-processing apparatus being characterized by the binder mover further including a ratchet gear configured to receive a driving force of the motor to rotate in a forward direction or a reverse direction; a driving force transmitter (43 to 48) configured to move the binder toward one side in the main scanning direction as the ratchet gear rotates in the forward direction and move the binder toward an opposite side in the main scanning direction as the ratchet gear rotates in the reverse direction; and a rotation limiter configured to move between a rotation allowing position at which the rotation limiter moves away from the ratchet gear to allow rotation in either of the forward direction and the reverse direction and a rotation limiting position at which the rotation limiter contacts the ratchet gear to allow rotation in the forward direction and restrict rotation in the reverse direction. a conveyor (10 to 19) configured to convey recording media on each of which an image is formed by an image forming apparatus; a tray configured to hold the recording media conveyed by the conveyor (10 to 19); a binder including a cartridge containing a plurality of staples, the binder being configured to bind the recording media on the tray with the plurality of staples in the cartridge; and a binder mover configured to move the binder in a main scanning direction that is orthogonal to a conveyance direction of the recording media conveyed by the conveyor (10 to 19), the binder mover including: a motor; the post-processing apparatus being characterized by the binder mover further including a ratchet gear configured to receive a driving force of the motor to rotate in a forward direction or a reverse direction; a driving force transmitter (43 to 48) configured to move the binder toward one side in the main scanning direction as the ratchet gear rotates in the forward direction and move the binder toward an opposite side in the main scanning direction as the ratchet gear rotates in the reverse direction; and a rotation limiter configured to move between a rotation allowing position at which the rotation limiter moves away from the ratchet gear to allow rotation in either of the forward direction and the reverse direction and a rotation limiting position at which the rotation limiter contacts the ratchet gear to allow rotation in the forward direction and restrict rotation in the reverse direction. a motor; the post-processing apparatus being characterized by the binder mover further including a ratchet gear configured to receive a driving force of the motor to rotate in a forward direction or a reverse direction; a driving force transmitter (43 to 48) configured to move the binder toward one side in the main scanning direction as the ratchet gear rotates in the forward direction and move the binder toward an opposite side in the main scanning direction as the ratchet gear rotates in the reverse direction; and a rotation limiter configured to move between a rotation allowing position at which the rotation limiter moves away from the ratchet gear to allow rotation in either of the forward direction and the reverse direction and a rotation limiting position at which the rotation limiter contacts the ratchet gear to allow rotation in the forward direction and restrict rotation in the reverse direction.