A bookbinding system includes an image forming apparatus and a bookbinding apparatus connected to the image forming apparatus. The bookbinding system includes an image forming unit to form an image on a recording sheet; a loading unit to load, as a bookblock stack, plural recording sheets on which images are formed; a bonding unit to form a booklet by bonding a cover with the bookblock stack; a setting unit to set a bookblock size, a cover size, and a finishing size; a cutting unit to cut the booklet bonded together with the cover into the finishing size; a stack thickness detection unit to detect a thickness of the bookblock stack; and a bookbinding permission/inhibition determination unit to determine permission/inhibition of a bookbinding operation based on a stack thickness detection result as well as the bookblock size, the cover size, and the finishing size set by the setting unit.