Abstract: An orthodontic expansion device for expanding a maxilla A and a maxillary dentition B includes: two hinges arranged with an interval; a screw; two intermediate members configured to be driven in directions of opening on a front end side with the respective hinges as fulcrums, by rotation operation of the screw; at least two arm members supported by the intermediate members and extending laterally and diagonally forward from the intermediate members; and a plurality of holding members supported by the arm members and configured to be attached to crowns of both lateral segments of the maxillary dentition B.