To block a heating medium liquid pressure of a main piping system which acts on a floor heating piping of each room and prevent water leakage of a floor heating piping especially for a lower floor without providing an emergency shut down device under automatic control or a water leakage detection device, or stop the operation automatically.

The end of each inlet and the end of each outlet of a heating medium liquid circulation pipe 7 are connected to a heating medium liquid supply header 5s and a heating medium liquid return header 6r in parallel respectively, while a heating medium bypass circuit is formed between a branch pipe 5 on the supply side and a branch pipe 6 on the return side. A directional control valve 10 and a control unit 11 are provided, which selectively bypass the heating value liquid of the supply side branch pipe 5 to the return side branch pipe 6 by way of a bypass pipeline 9 while a check valve 28 is provided, which prohibits a backward flow of the heating value liquid from the return line 4 to a heating value liquid circulation pipeline, thereby preventing the internal pressure of a main piping system from being spread to the heating value liquid return header 6r during the circulation shutdown of the main value liquid circulation pipe 7.