A recording sheet processing device includes a stack tray used, when a recording sheet gets jammed inside a subsequent finishing device, for collecting recording sheets left inside a preceding image forming device and recording sheets left inside a recording sheet feeding unit of the image forming device before those recording sheets reach the finishing device. A portion of a conveying path in the recording sheet processing device is opened so that the recording sheet that has jammed at the finishing processing side can freely fall down into a stack tray. Then, a conveying path switching claw is switched to a position for collecting subsequent recording sheets into the stack tray. Thus, subsequent recording sheets are collected in the stack tray without stoppage in conveyance.