To increase an ozone concentration, to increase the quantity of active oxygen produced by the photodecomposition of ozone, and to improve productivity and to reduce cost by improving treatment efficiency by introducing oxygen gas into treatment chamber to be treated when the surface of a substrate is made hydrophilic by the action between ozone and ultraviolet light.

When glass for liquid crystal is made hydrophilic, a low voltage mercury lamp 2 is installed in a treatment chamber 1, and an object 3 to be treated is supported by a height-variable holder 4. A treating gas is selected by a valve 7, with its flow rate adjusted by a flow meter 4. and sprayed to the object 3 by a spray nozzle 5. The exhaust gas, with its amount adjusted by a flow meter 9, is discharged outside an apparatus through an ozone decomposition filter 8 by a blower 10. A low voltage mercury lamp at least 1 W/cm in output per unit length is used as an ultraviolet ray generation source. The distance between the source and the object 3 is made 5-30 mm. In this way, a treatment time is curtailed as compared with treatment in the air, and the glass is made hydrophilic efficiently.