To reutilize washing water for electronic material dissolved oxidizing gas or reducing gas as pure water and to reduce a use quantity of the pure water in a washing process by being brought the washing water into contact with inert gas and converting it to inactive pure water.

The washing water for electronic material dissolved the oxidizing gas or the reducing gas is dropped as water droplets from the upper part of a gas-liquid contact tower 2 provided with a filler layer 1, and also the inactive gas is injected from the lower part of the gas-liquid contact tower 2 in a bubble form. The inactive gas is allowed to raise in a bubble state into treating water collected in the lower part of the gas-liquid contact tower 2, and the oxidizing gas or the reducing gas slightly remaining in the water is substituted with the inactive gas and is perfectly removed. The washing water for electronic material is brought into contact with the inert gas in the filler layer 1, and the oxidizing gas or reducing gas is removed from the washing water for electronic material which became in a thin film state, and the inactive gas is dissolved in the washing water, then the washing water is converted to the inactive pure water.