PURPOSE: To detect displacement of thin metal plate in the downstream of orifice based upon the pressure loss difference between front and rear of pipe orifice setting part provided in a water passage having a constant flaw value and also to measure accumulative consumed time and flow by deciding turn-on or turn-off of water.

CONSTITUTION: In a water passage 3 on the source water side, a thin metal plate 5 that supports a pipe orifice 4 and upstream side at the inner wall of the water passage 3, with downstream side being a free and, is provided. The passed source water passes through the orifice 4, and purified with a filter part 2, and then gets out of a water passage 3'. At that time, negative pressure takes place on the downstream side of the orifice 4, and the free end of the thin plate 5 changes its place toward wall surface direction of the water passage 3. This displacement is detected by an electrostatic capacity sensor 6, and time measurement starts assuming that as water conduction state. At no conduction of water, the thin plate does not change its place, and the sensor 6 detects that for stopping the time measurement. Thus, accumulated consumed time is measured, and since a water purifier has a constant flow value, the flow rate per a unit time is constant, so based upon this and the accumulated consumed time, accumulated used flow is obtained.