Provided is a device for cleaning oral cavity and a method for cleaning oral cavity capable of well cleaning stains such as plaque, tartar, and the like even in a narrow portion such as a clearance between teeth, a clearance between implants, and the like. A cover 11 includes a jetting orifice 11a and a discharge orifice 11b and covers a tooth 1 by leaving a clearance between the tooth 1 and the cover 11 so that the clearance can hold water. A jetting unit 12 is mounted in the jetting orifice 11a and includes a flow path 24a communicating with the clearance between the tooth 1 and the cover 11. The jetting unit 12 is configured to generate cavitation bubbles by water flowing toward the clearance in the flow path 24a and jets the cavitation bubbles toward the inside of the cover 11. The flow path 24a includes a small diameter part 24b having a flow path diameter smaller than that on the upstream side and an enlarged part 24c having a flow path diameter larger than that of the small diameter part 24b. A discharge unit 13 discharges water in the clearance between the tooth 1 and the cover 11 from the discharge orifice 11b.
