To provide a method and an apparatus for producing ozone water, in each of which ozone is utilized efficiently to increase the ozone concentration in the ozone water.

A vessel 51 having an openable closed system is arranged and the ozone water is produced by introducing an ozone-containing gas and purified water into the vessel 51 and increasing the pressure of the closed system to dissolve ozone in the purified water. The vessel 51 includes: a valve V1 for introducing the ozone-containing gas; a valve V2 for introducing the purified water; and a valve V3 for discharging the ozone water so as to form the openable closed system. The volume of the vessel 51 is made variable and adjusted by a movable wall part 55 so that the pressure of the closed system becomes a predetermined value. A warming means is arranged suitably in the vessel 51 and in a purified water supply system so that the temperature in the vessel 51 and that in the purified water supply system become predetermined values. Ozone gas of 99% ozone concentration is exemplified as the ozone-containing gas.