A water electrolysis apparatus applies an electrolysis voltage between current collectors disposed on the respective sides of an electrolyte membrane thereby to electrolyze water to generate oxygen in an anode electrolysis chamber and hydrogen in a cathode electrolysis chamber under a pressure higher than a normal pressure. The water electrolysis apparatus is shut down by applying a voltage between the current collectors after the cathode electrolysis chamber stops supplying the hydrogen, reducing a pressure in at least the cathode electrolysis chamber while the voltage is being applied, and stopping applying the voltage when the pressure in the cathode electrolysis chamber is equal to a pressure in the anode electrolysis chamber.