A bookbinding system to bind together a batch of sheets transported from an image forming apparatus. The bookbinding system includes a punch unit to form a predetermined number of ring holes in a predetermined portion along a side of the sheets to be bound one by one or in a batch, a ring-binding unit disposed downstream from the punch unit in a direction in which the sheet is transported to insert rings of a ring member into the ring holes formed on the batch of sheets by the punch unit, a ring detector disposed at a portion where the ring member is set to detect a type of the ring member, and a determination unit to determine whether or not an ring-binding operation is executable based on a type of the ring member and a size of the sheets to be bound together.