Ozone treatment device and ozone treatment method to prevent the sealing member from being deteriorated due to ozone that airtightly seals the processing space for performing the ozone treatment

To prevent the sealing member from being deteriorated due to ozone that airtightly seals the processing space for performing the ozone treatment. An ozone treatment device (100) includes a light source unit (10) having a window member (12) for ultraviolet rays to penetrate therethrough, the ultraviolet rays are emitted through the window member (12); a stage (21) is configured opposite to the window member (12) to place an object to be treated (i.e. workpiece (W)); a sealing member (17), which is a space between the window member (12) and the stage (21) and is used to make the workpiece placed on the stage (21) to be airtightly enclosed in the processing space with the ozone-containing ambient environment and exposed to ultraviolet rays emitted from the light source unit (10); and a shielding gas supply unit consisted of a shielded gas supply channel (16d) and a shielding gas supply port (16e), whereby gas for protecting the sealing member (17) is supplied along at least a part of the sealing member (17).