[Problem] To provide a device for washing oral cavity and a method for washing oral cavity, whereby stains such as plaque and dental calculus can be effectively removed even from a narrow space such as a gap between teeth or a gap of an implant. [Solution] A device for washing oral cavity, said device comprising a cover (11) provided with an injection hole (11a) and a discharge hole (11b), wherein the cover (11) covers a tooth (1) while leaving a space between the cover (11) and the tooth (1) so that water can be held in the space. To the injection hole (11a), an injection means (12), which is provided with a channel (24a) connected to the space between the tooth (1) and the cover (11), is attached. The injection means (12) is configured so that cavitation bubbles can be generated when water flows in the channel (24a) toward the space and the thus generated cavitation bubbles are injected toward the inside of the cover (11). The channel (24a) has a small diameter part (24b) with a channel diameter being smaller than the channel diameter in the upstream side and an enlarged part (24c) with a channel diameter being larger than the channel diameter in the small diameter part (24b). A discharge means (13) is provided so that water within the space between the tooth (1) and the cover (11) is discharged through the discharge hole (11b).[Problème] Décrire un dispositif pour laver une cavité orale et un procédé pour laver une cavité orale, de telle manière que les taches telles que la plaque et le tartre dentaires puissent être efficacement éliminées même depuis un espace étroit tel quun espacement entre des dents ou un espacement dun implant.[Solution] La présente invention concerne un dispositif pour laver une cavité orale, ledit dispositif comprenant un couvercle (11) pourvu dun trou dinjection (11a) et dun trou de décharge (11b), le couvercle (11) recouvrant une dent (1) tout en laissant un espace entre le couvercle (11) et la dent (1) de sorte que leau puisse être main
