To effectively remove the problem that impurities or unnecessary substances dissolved in a liquid to be treated are not removed in conventional purifying treatment using ozone.

In a liquid purifying method using ozone, a required amount of the liquid to be treated is housed in a treatment tank having an ultraviolet lamp arranged therein and a mixed gas of ozone and air is successively supplied in a state of fine air bubble groups from the bottom part of the treatment tank for the purpose of aeration to be brought into contact with the liquid to be treated under stirring. The successively supplied fine air bubble groups are irradiate with ultraviolet rays to successively form nascent oxygen and active oxygen produced from ozone contained in the fine air bubble groups. Impurities are oxidized, reduced and sterilized or bonded to be removed by the repeated contact of successively formed nascent oxygen and active oxygen with the stirred liquid to be treated. By this method, the liquid to be treated is successively aerated by the ozone-containing fine air bubble groups and stirred in the treatment tank, the fine air bubble groups are irradiated with ultraviolet rays from the ultraviolet lamp to efficiently form active oxygen and the like from ozone of the fine air bubble groups and impurities are reacted with active oxygen and the like to be separated and removed.