To provide a water purifier that can effectively clean a filter medium with respect to organic matter or adhesive materials, such as bacteria.

The water purifier 100 includes a housing 10, the filter medium 20, a fine ozone bubble generator 30, an introduction portion 40, and a lead-out portion 50. The housing 10 has a cylindrical shape and an inner surface 13. A space having a predetermined distance is provided between the filter medium 20 and the inner surface 13. A liquid containing fine bubbles having ozone introduced from the introduction portion 40 into the housing 10 flows into the housing 10 in the circumferential direction along the inner surface 13, and flows inside the housing 10 so as to rotate in the space. The liquid flowing inside the housing 10 flows out into the lead-out portion 50 in the circumferential direction along the inner surface 13.