PURPOSE: To extend the distance of a transmission line without slowing down the transmission speed by configurating the method with a step sending a priority part of a pulse width depending on the range of the transmission line when the transmission line is idle and a step sending a data part with a pulse width narrower than the pulse width for the priority part when its own station has a token.

CONSTITUTION: A priority part whose pulse width is W2 depending on the range of a transmission line in a transmission signal is sent at a first step when the transmission line is idle and a data part whose pulse width is W3 narrower than the pulse width of the priority part in the transmission signal is sent at a 2nd step when its own station has a token. The pulse width Ws of the data part is set shorter than the pulse width W2 of the priority part of the transmission signal in this way and a bit discrimination sampling location and a sampling period of the data part are set again simultaneously at the start of reception of the data part. Thus, the range of the transmission line is extended without slowing down the transmission speed and an error in the priority part and the data part is reduced.