An assembly jig for use in assembly of a large structure, wherein the assembly jig is arranged to support the large structure thereon and comprises: an upper jig frame that is suitable for being provided above a longitudinal outer edge of the large structure; a lower jig frame that is suitable for being provided below the longitudinal outer edge of the large structure; a connecting jig frame (5,5a,5b) that connects the upper jig frame and the lower jig frame to each other; three supporting means for supporting the lower jig frame from below; and a jig leg portion that is provided perpendicular to a direction in which the lower jig frame extends and parallel to a ground surface, wherein the supporting means are provided at only three portions that are respectively located at two end portions of the jig leg portion and at the lower jig frame, wherein arrangement positions of the supporting means provided at the three portions form a substantially triangular shape when seen from above, characterised in that each of the supporting means has a supporting member that is provided such that a substantially central portion thereof in a direction in which the supporting member extends is supported by a swing member provided on the jig leg portion or the lower jig frame and such that the supporting member extends in a direction perpendicular to a direction in which the jig leg portion or the lower jig frame extends; and legs or wheels that are provided under the supporting member and are arranged to come into contact with the ground surface, wherein a plurality of intermediate supporting members are provided in one or more layers under each supporting member such that substantially central portions thereof in directions in which the intermediate supporting members extend are supported at the two end portions of the supporting member by respective swing members, and wherein the plurality of intermediate supporting members of a respective layer of the one or more layers are provided so as to extend in a direction perpendicular to a direction in which the supporting member or an intermediate supporting member in a layer located above extends. an upper jig frame that is suitable for being provided above a longitudinal outer edge of the large structure; a lower jig frame that is suitable for being provided below the longitudinal outer edge of the large structure; a connecting jig frame (5,5a,5b) that connects the upper jig frame and the lower jig frame to each other; three supporting means for supporting the lower jig frame from below; and a jig leg portion that is provided perpendicular to a direction in which the lower jig frame extends and parallel to a ground surface, wherein the supporting means are provided at only three portions that are respectively located at two end portions of the jig leg portion and at the lower jig frame, wherein arrangement positions of the supporting means provided at the three portions form a substantially triangular shape when seen from above, characterised in that each of the supporting means has a supporting member that is provided such that a substantially central portion thereof in a direction in which the supporting member extends is supported by a swing member provided on the jig leg portion or the lower jig frame and such that the supporting member extends in a direction perpendicular to a direction in which the jig leg portion or the lower jig frame extends; and legs or wheels that are provided under the supporting member and are arranged to come into contact with the ground surface, wherein a plurality of intermediate supporting members are provided in one or more layers under each supporting member such that substantially central portions thereof in directions in which the intermediate supporting members extend are supported at the two end portions of the supporting member by respective swing members, and wherein the plurality of intermediate supporting members of a respective layer of the one or more layers are provided so as to extend in a direction perpendicular to a direction in which the supporting member or an intermediate supporting member in a layer located above extends.