PURPOSE: To unitarily manage the alarm of a bypass condition at the time of connecting multiple lines with a pair of network ports(NP) so as to shorten time till bypass, on a bypass system when a fault occurs to a communication equipment using a high speed digital line (HDV2 network).

CONSTITUTION: At the time of transferring data between a main station 1a executing multiplex access and plural salve stations 2-1, 2-2... by using the high speed digital line, a bypass source is switched to a bypass destination by allocating a first specified signal and a second specified signal to respective line numbers and the state of the respective salve stations 2-1, 2-2... is unitarily managed by making the first specified signal and the second specified signal correspond to the respective line numbers in the main station 1a in a form where the respective slave stations 2-1, 2-2... have the bypass source and the bypass destination, and the bypass source and the bypass destination have the detection functions of the first specified signal and the second specified signal in a time slot unit.