PURPOSE: To accurately detect the water pressure and a flow rate using a semiconductor pressure transducer in an ion water formation apparatus.

CONSTITUTION: This flow rate detection mechanism is constituted of the water pressure detecting pitot tube 1 provided in a tap water inflow pipe, semiconductor pressure transducers 2, 3 accurately measuring detected water pressure, an A/D converter 4 subjecting water pressure measuring output to A/D conversion, a pressure reducing valve 5 reducing the pressure of a water pipe and a control part 6 inputting a measured value from the A/D converter to calculate the flow velocity and flow rate of inflow water to perform pH adjusting control by the control of the electrolytic level of an electrolytic power supply 25 or the flow rate control due to the pressure reducing valve.