Abstract: The present invention relates to a loop network arranged by loop-connecting a control station and a number of substations through a main transmission path where at least one of the substations comprises a branch station inserting and coupling another station into the main transmission path as a lobe or subloop. In order to prevent an out-of-step condition of the main transmission path, resulting from a failure in the lobe or subloop, the branch station includes a frame buffer for normally selecting the signal from the lobe or subloop and selecting the signal from the main transmission path during detection of a failure and on a bypass command, and for accumulating the selected signal in units of a single frame, and a mechanism for supplying the accumulated signal to the main transmission path.