A communication apparatus in which subscriber devices are connected to a network device. The network device creates a message for setting up the effectiveness of sending permission information for each subscriber device and waits for the sending of polling information for allocating sending permission for each subscriber device by using the sending permission information for a predetermined time determined considering the processing time of each subscriber device from the timing at which the sending of the message is ended. When detecting the cut-off of an input cell from each subscriber device, the network device can wait for a predetermined time from the timing at which the sending of the message and polling information is ended. Further the network device can wait for the switching of the input cut-off detection/sending permission information by exchanging messages mutually.
