To decrease an accident of continuous large-quantity water leakage in a broken part by incorporating a check valve which can be closed on receiving fluid pressure of the upstream in a coupling main body, and keeping the check valve element in the valve closing state in the ordinary condition.

In a coupling main body 1 interposed in a branch pipe connecting part near the main pipe, in the ordinary condition, a valve element 5e of a check valve 5 is inhibited from sitting on a valve seat by a baffle rod 4b projected from a baffle rod structure 4 to keep the valve opening state, thereby sustaining a flow from the main pipe side piping 7. When side pressure above regulated is applied to the downstream branch pipe 7' near the coupling due to any cause, a connecting part between the flange part 3a and the sleeve part 3b of the flanged sleeve 3 is cut to be separated and opened before the branch pipe 7' is broken. Accordingly, the baffle structure 4 is moved backward with the sleeve part 3b, the support force for the valve element 5e by the buffle plate 4b is lost so that the valve element 5e is seated at a stroke by water pressure of the primary side and the reaction force of the spring so as to surely inhibit leakage and jetting of the upstream fluid.