To provide a booklet stacker capable of reducing a space without declining productivity.

This booklet stacker comprises a booklet receiving means receiving booklets bound by a booklet binding device in a booklet receiving position and a booklet stacking means capable of stacking a plurality of booklets received by the booklet receiving means and having a transfer mechanism capable of transferring the booklets. The booklet receiving means is provided with a receiving mechanism transferring the booklets received in the booklet receiving position to a predetermined position; and with a delivery mechanism transferring the booklets transferred in the predetermined position downward from the predetermined position, delivering the booklets to the booklet stacking means and returned to the predetermined position. The booklet stacker is provided with a drive mechanism driving a booklet carrying means when a moving carriage attachable to/detachable from the booklet stacker and having the booklet carrying means receiving the booklets stacked on the booklet stacking means from the transfer mechanism is mounted to the booklet stacker.