A plate material is formed into a height difference adjusting member having a J-shape such that its shim portion and resilient support portion are opposed to each other. The height difference adjusting member is mounted on a spar such that the shim portion and the resilient support portion are resiliently mounted to a flange of the spar. A rear end of a leading edge skin is fixed to the flange by a fastener in a state where the shim portion of the height difference adjusting member is interposed between the leading edge skin and the flange. The shim portion adjusts a difference in height between a front end of a main body skin and the rear end of the leading edge skin. Even if a large number of height difference adjusting members are mounted on the spar, the height difference adjusting members do not fall off and are not displaced.