To provide a printing system capable of being connected between an image forming apparatus and an accessory device and between accessory devices, without having to use an interface cable and not transmitting/receiving a signal normally, when mechanical positioning is not established.

In the printing system, constituted by connecting a plurality accessory devices to the image forming apparatus in series, the system is provided with a radio communication part for providing/receiving signals to/from the image forming apparatus and the accessory devices, respectively, and protruded and recessed parts for performing relative positioning with respect to a facing surface to be connected. The radio communication part is arranged inside the protruded part, and only when the protruded part of the connected device is fitted into the recessed part, the radio communication is performed normally between the devices.