An image forming system includes an image forming apparatus and a post-processing apparatus that performs post-processing on sheets discharged from the image forming apparatus. The image forming system includes a feeding unit configured to store a plurality of sheets and successively feed the sheets; a stack unit configured to stack sheets processed by the post-processing apparatus; a state detection unit configured to detect a predetermined state of the stack unit; and a control unit configured to restrict the number of sheets fed from the feeding unit so that the number of sheets existing in a sheet conveyance path extending from the feeding unit to the stack unit does not exceed a predetermined number. The predetermined number is the number of sheets that the post-processing apparatus can receive from the image forming apparatus after detection of the predetermined state by the state detection unit.