According to the invention, in the transport path between the input device and the output device, at least one intermediate buffer is arranged that serves as input device and as output device. The input device, the output device and the intermediate buffer are positioned adjacent to the conveyor belt and operated by the control device in such a way, that sheets forwarded from the input device or sheets stocked in the intermediate buffer are coupleable pneumatically to the lower side of the conveyor belt, and that sheets pneumatically attached to the lower side of the conveyor belt are selectively decoupleable at the intermediate buffer or at the output device.