Air filtering apparatus having mechanism for detecting water exchange timing

An air filtering apparatus for electrolyzing water to generate electrolytic water containing active oxygen specifies and filtering air by using the electrolytic water, comprising:nan electrolytic tank for generating electrolytic water;a gas-liquid contact member to which electrolytic water from the electrolytic tank is supplied to bring air into contact with the electrolytic water, thereby filtering the air;a water receiving tray that has a water receiving unit for receiving used electrolytic water discharged from the gas-liquid contact member and a water stock unit which is joined with the water receiving unit, the water stock unit having a deeper bottom than the water receiving unit to stock the used electrolytic water discharged from the gas-liquid contact member;a circulating pump for circulating the electrolytic water stocked in the water stock unit to the electrolytic tank;an electrical conductivity detecting unit for detecting the electrical conductivity of the circulated electrolytic water;a drain pipe that is connected to the water stock unit and discharge the electrolytic water stocked in the water stock unit to the external;a drain valve that is connected to the drain pipe and discharges the electrolytic water stocked in the water stock unit from the drain pipe to the external by an opening/closing operation thereof; anda controller for controlling the opening/closing operation of the drain valve and opening the drain valve when the electrical conductivity detected by the electrical conductivity detecting unit is out of a predetermined range, thereby discharging the electrolytic water stocked in the water stock unit to the external.