PURPOSE: To transmit with priority a frame during processing of backoff by limiting the start of transmission of frame of a new station during the backoff processing time in a bus type local area network.

CONSTITUTION: When stations STN1 and STN2 transmit a data of a transmission frame to a coaxial cable 4 at the same time, collision is detected at each transceiver 2 and it is informed to the STN1 and STN2 via a collision detection signal line 53. The state of collision is detected by each transceiver 2 and it is informed on the signal line 53 to STN3∼STNn not performing frame transmission. The STN3∼STNn become in the state of transmission stop after this point of time, and after the STN1 and the STN2 stop the frame transmission after a prescribed time, they transmit the retransmission frame by means of the backup processing with priority. When a carrier by the retransmission frame is detected twice by a carrier detecting circuit 13, the STN3∼STNn discriminate that the frame transmission from the STN1 and STN2 is finished, and release the transmission stop state.