from the bonding cart 31 following the curing of the adhesive agent a sixth step of positioning the upper skin assembly 67 on the assembly jig 71 on the basis of positioning pins 73 73 77 77 disposed on the assembly jig 71 a seventh step of disposing a plurality of ribs 14 in specified positions on this upper skin assembly 67 and then fastening the upper skin assembly 67 and plurality of ribs 14 using rivets and an eighth step of disposing the lower skin 16 in a specified position with respect to the upper skin assembly 67 to which the plurality of ribs 14 has been fastened by rivets and then fastening the upper skin assembly 67 and ribs 14 to the lower skin 16 using rivets as a result since the lower skin 16 is fastened using rivets to the upper skin assembly 67 the upper skin assembly 67 and lower skin 16 can be strongly fastened and the rigidity of the main wing can be improved in the present invention when the abovementioned front spar 12 and rear spar 13 are positioned on and fastened to the abovementioned upper skin 11 a beam pressing jig 41 is fastened to the upper parts of the front spar 12 and rear spar 13 and the front spar 12 and rear spar 13 are held as a result deformation of the front spar 12 and rear spar 13 during the curing of the adhesive agent is prevented.