To immediately detect water leakage for informing by inputting measured data by a water meter provided on a connection end of a distributing pipe and a measuring meter provided on a water feed end of a water inlet pipe for obtaining difference between both data and outputting a water leakage detection signal when the difference exceeds an allowable range.
Measured data of a water department meter 4, that is a pulse signal, is transmitted to a water leakage detecting controller 8. Then a measuring meter 7 also transmits measured data, that is a pulse signal, to the controller 8. The controller 8 receives measured data from both meters 4, 7 for obtaining difference in a data comparison part, and then compares the difference with an allowable value preset in a data setting part. If water leaks in a middle point 2a of a water inlet pipe 2, the difference exceeds the allowable range, and a detection part 8c outputs a water leakage detection signal as water leakage occurrence. The signal causes an alarm 9 to activate, an alarm lamp 10 to light up, and informs water leakage occurrence, so that an operator closes a stop valve.