To provide a water flow detector which minimizes water damage during a malfunction of a sprinkler head and never outputs water signals when a valve disc in the water flow detector is slightly opened because of a reduced pressure in a secondary pipe arrangement in the water flow detector installed in a sprinkler fixture capable of controlling to open and close a control valve, which remains in an open state all the time, placed on a pipe arrangement where the water flow detector is disposed, and is opened and closed by electric signals, by subjecting fire signals output when a fire sensor is activated and water flow signals output when the water flow detector is activated to signal processing in a control device and by outputting the signals to the control valve.

The water flow detector has a structure to output signals from a switch by displacement due to an opening action of the valve disc in the water flow detector and is equipped with a first switch outputting signals immediately when the valve disc is displaced at least a prescribed range and a second switch outputting signals after a lapse of a delay time.