To prevent both wings from causing left-right-unbalanced operation, by connecting the outer end of a link arm with two matched mobile wing surfaces of both wings, interconnecting their inner ends, and operating the matched mobile wing surface left-right symmetrically.

Inner slats 3a of both side wings 1 are interconnected through two inner link arms 10, and each of slats 3a is connected with an inner swing arm 6 of a slat 3a at its outer end. The inner ends of the inner link arms 10 are connected with a crank 11 which is placed on a center line(CL) of an airplane. Rotation of the crack 11 moves two inner link arms 10 inward or outward, and transfers inner slats 3 into operation condition or accommodation condition. Interconnection of these two inner slats 3a operates the both slats 3a synchronously. Adjacent slats 3a and 3b, and 3b and 3c of each wing are interconnected by an outer link arm 12.