There is provided a connection apparatus for connecting an image forming apparatus and a plurality of sheet post-processing apparatuses. This connection apparatus has a flapper portion for switching a plurality of conveying paths going toward the plurality of sheet post-processing apparatuses. Sensors are provided near inlet rollers and near output rollers, respectively. Outputs of the sensors are inputted to a wired OR circuit, so that an output of the wired OR circuit is supplied to a CPU of one of the connected sheet post-processing apparatuses.