A guide portion guides a binding unit in a first direction and a second direction. The guide portion includes a pair of first wall portions, a pair of second wall portions, a pair of third wall portions, and a restricting portion. A first protrusion is engageable between the pair of first wall portions and between the pair of second wall portions. A second protrusion is disposed upstream of the first protrusion in the first direction, and is engageable with the pair of first wall portions and the pair of third wall portions. The restricting portion restricts entry of the first protrusion from between the pair of first wall portions to between the pair of third wall portions and permits entry of the second protrusion from between the pair of first wall portions to between the pair of third wall portions.

The present invention provides a transport guide drive mechanism that corrects the transport state in a paper sheet transport device including a wide transport surface that can be used in common for paper sheets with different width dimensions, to a normal state while preventing a deformation or a damage of the paper sheets during continuous and unintermittent transport. The transport guide drive mechanism includes transport guides 310 that are arranged along both side edges of a transport surface 11 in a width direction to oppose each other and that respectively guide both side edges of a paper sheet to be transported, an advancing/retreating mechanism 350 that causes the transport guides to synchronously protrude and retract in a predetermined direction, stoppers 440 each of which defines a protruded position where an associated one of the transport guides 310 is most protruded from the transport surface 11 and a retracted position retracted from the protruded position toward the transport surface, and a DC motor 450 that drives the advancing/retreating mechanism 350.