Abstract: A data transmission system capable of eliminating a local traffic jam comprises a plurality of packet controllers each including a queue buffer for storing packets, the packet controllers being arranged in one-to-one correspondence with channels of a multiplexed transmission line, and an adapter for transmitting an object packet to a packet controller selected in accordance with a priority included in the object packet and an average priority of the packets stored in each queue buffer. Each packet controller receives the object packet from the adapter, stores the received packet, reads out the stored packets from the queue buffer, the number of which is determined in accordance with transition of a degree of traffic jam of the corresponding channel, and transmits the readout packets to other stations through the corresponding channel. Each packet controller calculates an average priority of the packets stored in the queue buffer.