To construct a system automatically closing water supply piping after detecting water leakage by monitoring water supply pipes in a multiple dwelling unit.

A water leak sensor 3 is provided for respective water supply pipes 5, 6, 7, 8 for each house unit branched from the main water pipe in multiple dwelling units such as apartment houses or dwelling units individually rented or owned with a plurality of floors. And it has a control section 14 which judges the presence or absence of a water leak after receiving electrical signals generated after detecting a water leak by a water leak sensor 3 and an automatic valve 15 which closes water supply pipes 5, 6, 7, 8 after the control section 14 has judged water leakage.