A transmission apparatus for stably transmitting or receiving data of high priority is provided. In the transmission apparatus of the present invention, processing of the priority packet to be transmitted and processed by priority and processing of the non-priority packet are conducted separately. At transmission side, the above-mentioned priority packet is transmitted by priority by making its average transmission interval shorter than its average generation interval, and said non-priority packet is transmitted during the transmit margin period caused by the above-mentioned processing. At receive side, in the layer of processing the receive frame as a layer lower than the layer of processing the priority packet and non-priority packet, the priority packet and the non-priority packet is sorted based on the communication protocol header of the receive packet stored in the receive frame, and processing of the priority packet and that of the non-priority packet are conducted separately.