fig6 a the adhesive agent is cured in a process of pressing and heating the bonding sites described later in a state in which the beam pressing jig 41 indicated by an imaginary line is fastened to the front spar 12 and rear spar 13 subsequently almost no deformation occurs in the front spar 12 or rear spar 13 even in a state in which the beam pressing jig 41 is removed as is shown in fig6 b almost no falling over deformation occurs in the front spar 12 or rear spar 13 even in a state in which the beam pressing jig 41 indicated by an imaginary line is removed from the front spar 12 and rear spar 13 fig6 c shows a state following the curing of the adhesive agent in a pressing and heating process performed in a state in which the beam pressing jig 41 fig6 a is not fastened to the front spar 12 or rear spar 13 an undulation deformation is generated in the front spar 12 and rear spar 13 as is shown in fig6 d in the front spar 12 and rear spar 13 the sides of the respective flanges 12 b and 13 b have fallen over toward the inside fig7 shows a sectional view of a state in which the areas around the bonding sites between the upper skin 11 and front spar 12 and rear spar 13 are covered by a backing film the areas around the bonding sites between the upper skin.