PURPOSE: To prevent the disuse of data when the received data collide against each other in a data branch circuit in regard of a polling data collection system.

CONSTITUTION: The data input part of each interface part of a data branch circuit is provided with a data detecting part 1 which receives the input data and produces a detection signal, a selector part 2 which changes the transmitting direction of the input data, a storage part 3 which stores the input data, and a control part 4 which controls the operations of both parts 2 and 3 in accordance with the detection signal sent from the part 1 or another interface part. While a certain interface part is receiving the input data, the input data are sent to another interface part via the part 2. While the latter interface part is producing a detection signal, the input data are supplied to the part 3 via the part 2 and stored in the part 3. When the precedent data are transmitted and received, the stored data are read out and sent to each of other interface parts.