An oral cavity washing device comprising: a body unit including a pump from which a washing liquid is discharged, wherein the body unit includes a first case which accommodates the pump ; a tube connected to the body unit so as to make the discharged washing liquid flow through the tube ; a washing unit connected to the tube so as to discharge the washing liquid; and a joining portion which joins the body unit and the washing unit to each other by a magnetic force, wherein the joining portion includes a first joining portion mounted on the body unit , and a second joining portion mounted on the washing unit , one of either the first joining portion or the second joining portion includes a magnet , and the other of either the first joining portion or the second joining portion includes a magnet or a ferromagnetic , the body unit further includes a recessed portion , the recessed portion has a shape corresponding to a shape of an outer shell of the washing unit , in a state where the washing unit is joined to the body unit by the joining portion , the washing unit is disposed on the recessed portion of body unit , the recessed portion is formed so as to extend in a height direction of the body unit , the washing unit includes a second case having a grip portion , and a nozzle mounted on the second case so as to discharge the washing liquid, and the second joining portion is mounted on the grip portion , characterized in that the second case includes a first end portion on which the nozzle is mounted, and a first end surface which is formed on the first end portion , and in a state where the washing unit is mounted on the body unit , the first end surface is disposed on substantially a same plane as an upper surface of the body unit . a body unit including a pump from which a washing liquid is discharged, wherein the body unit includes a first case which accommodates the pump ; a tube connected to the body unit so as to make the discharged washing liquid flow through the tube ; a washing unit connected to the tube so as to discharge the washing liquid; and a joining portion which joins the body unit and the washing unit to each other by a magnetic force, wherein the joining portion includes a first joining portion mounted on the body unit , and a second joining portion mounted on the washing unit , one of either the first joining portion or the second joining portion includes a magnet , and the other of either the first joining portion or the second joining portion includes a magnet or a ferromagnetic , the body unit further includes a recessed portion , the recessed portion has a shape corresponding to a shape of an outer shell of the washing unit , in a state where the washing unit is joined to the body unit by the joining portion , the washing unit is disposed on the recessed portion of body unit , the recessed portion is formed so as to extend in a height direction of the body unit , the washing unit includes a second case having a grip portion , and a nozzle mounted on the second case so as to discharge the washing liquid, and the second joining portion is mounted on the grip portion , characterized in that the second case includes a first end portion on which the nozzle is mounted, and a first end surface which is formed on the first end portion , and in a state where the washing unit is mounted on the body unit , the first end surface is disposed on substantially a same plane as an upper surface of the body unit . <EOS>