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.