PURPOSE: To recognize a position of each station on a transmission line only with transmission processing of a transmission frame by storing a transmission frame representing the presence of reception of a reply frame to other stations than sending a transmission frame and locating the connection sequence of the stations on the transmission line based on the result of recording.

CONSTITUTION: When a connection position confirmation frame sent at first by a #3 station 23 is a frame addressed to a #1 station, the frame is received by all stations except the station #3 at lower positions than the station 23 and stored. Then a #1 station sends a reply frame corresponding to the connection positioncon firmation frame. The reply frame sent by a #1 station 21 is received by all stations at lower position than the #1 station 21 and recorded to a storage section of each station by a reply frame from the #1 station 21. When the reception of the reply frame from the #1 station 21 is finished, the #3 station 23 sends a connection position confirmation frame to the #2 station 22. In this case, the connection position confirmation frame is received by all stations and the reply frame from the #2 station is reached to the #3 station 23 only.