To provide a treatment device for safely and efficiently performing treatment using ozone-containing gas (ozone treatment).

In this treatment device, bubble-like ozone-containing gas is brought into contact with a diseased part in a water medium. The device is characterized in that: (i) a specified treatment chamber is provided; (ii) a specified water medium is stored in the treatment chamber; (iii) a specified void part 5 is provided; (iv) a specified opening part 4 is provided on the upper part of the treatment chamber; (v) the bottom of the treatment chamber is provided with an ozone-containing gas diffuser member 13; (vi) a specified intake pipe 6 is attached to the top plate or the upper peripheral wall of the treatment chamber; and (vii) an intake member 8 is attached to the intake pipe 6.