PURPOSE: To reconstitute a data way at a high speed by sending the state signal of one station to its adjacent station in response to a circuit reconstitution start signal, and changing states of connections with a circuit on the basis of a state signal from the adjacent station in response to a circuit reconstitution end signal.

CONSTITUTION: When a monitor station starts reconstituting operation in a dual loop data way ststem, a start command is outputted to the circuit 1. If a fault occurs in a station (k), the start command does not arrives to the station (k). Stations (i) and (j) receive the start command and output state answer signals to their upstream stations through the circuit 2 respectively. When the monitor station outputs an end command to the circuit 1, each station decides on whether the circuit connected to the station is placed in loop-back mode or forward mode on the basis of the state answer signal from the downstream station.