A drill assistance device comprising: a drill guide device that serves as a guide for a drill when forming a plurality of holes (h) from a curved surface of a hard palate having the curved surface; and a guide sleeve that is fitted in the drill guide device in an attachable and detachable manner, the drill guide device comprising: a guide frame unit that is adapted to be arranged on the curved surface and formed by connecting a plurality of tubular guide frames to each other; a fixing member to be capped on a tooth of a patient; a connecting portion that connects the guide frame unit and the fixing member and determines arrangement of the guide frame unit on the curved surface with reference to the tooth; and at least one protruding portion that protrudes from at least one portion of the guide frame unit on a side opposite to a side facing the curved surface and holds the guide sleeve inserted in any of holes inside the guide frames, the guide sleeve comprising: a tubular sleeve main body having an inner diameter that allows the drill to be inserted and an outer diameter that allows the sleeve main body to be inserted in any of the holes of the guide frames; a water injection slit that is provided in a direction in which the sleeve main body extends; and projecting portions that are provided on an outer peripheral surface of the sleeve main body and are each fitted in at least one recessed portion provided in the at least one protruding portion when the sleeve main body is inserted in any of the holes of the guide frames, wherein a sum of a number of the at least one recessed portion and a number of the projecting portions is three or more, wherein when the guide sleeve is inserted in any of the guide frames, one of the at least one recessed portion and one of the projecting portions can be fitted to each other so that the water injection slit faces an oral cavity vestibular side. a drill guide device that serves as a guide for a drill when forming a plurality of holes (h) from a curved surface of a hard palate having the curved surface; and a guide sleeve that is fitted in the drill guide device in an attachable and detachable manner, the drill guide device comprising: a guide frame unit that is adapted to be arranged on the curved surface and formed by connecting a plurality of tubular guide frames to each other; a fixing member to be capped on a tooth of a patient; a connecting portion that connects the guide frame unit and the fixing member and determines arrangement of the guide frame unit on the curved surface with reference to the tooth; and at least one protruding portion that protrudes from at least one portion of the guide frame unit on a side opposite to a side facing the curved surface and holds the guide sleeve inserted in any of holes inside the guide frames, a guide frame unit that is adapted to be arranged on the curved surface and formed by connecting a plurality of tubular guide frames to each other; a fixing member to be capped on a tooth of a patient; a connecting portion that connects the guide frame unit and the fixing member and determines arrangement of the guide frame unit on the curved surface with reference to the tooth; and at least one protruding portion that protrudes from at least one portion of the guide frame unit on a side opposite to a side facing the curved surface and holds the guide sleeve inserted in any of holes inside the guide frames, the guide sleeve comprising: a tubular sleeve main body having an inner diameter that allows the drill to be inserted and an outer diameter that allows the sleeve main body to be inserted in any of the holes of the guide frames; a water injection slit that is provided in a direction in which the sleeve main body extends; and projecting portions that are provided on an outer peripheral surface of the sleeve main body and are each fitted in at least one recessed portion provided in the at least one protruding portion when the sleeve main body is inserted in any of the holes of the guide frames, a tubular sleeve main body having an inner diameter that allows the drill to be inserted and an outer diameter that allows the sleeve main body to be inserted in any of the holes of the guide frames; a water injection slit that is provided in a direction in which the sleeve main body extends; and projecting portions that are provided on an outer peripheral surface of the sleeve main body and are each fitted in at least one recessed portion provided in the at least one protruding portion when the sleeve main body is inserted in any of the holes of the guide frames, wherein a sum of a number of the at least one recessed portion and a number of the projecting portions is three or more, wherein when the guide sleeve is inserted in any of the guide frames, one of the at least one recessed portion and one of the projecting portions can be fitted to each other so that the water injection slit faces an oral cavity vestibular side.