To provide an environment in which the position of a belt-like surplus part can be set, in bookbinding processing to form a booklet by attaching a ring binder composed of the flat belt-like surplus part and a plurality of rings arranged along the longitudinal side of the belt-like surplus part, and to improve the productivity by starting the printing operation before finishing reading all the originals.

The image forming system includes: a ring bookbinding section including also a ring binder section configured to form the booklet by performing the bookbinding processing to attach to a bundle of sheets, the ring binder composed of the flat belt-like surplus part and the rings arranged along the longitudinal side of the belt-like surplus part; and a control section configured to control an image forming section so that a printing order based on image data may be different from a page order of the image data acquired by an image data acquisition section, on the basis of the setting information on the insertion position of the belt-like surplus part into the booklet to be formed.