To provide a skeleton structure in which one structure is coupled to a side part of another structure while ensuring the high rigidity, and to provide a skeleton structure in which the friction stir welding can be applied to even a part where the two structures are intersected vertically.

The skeleton structure 1 has a side frame 2 (a hollow structure) having an insertion hole 22 in a side face 21 thereof, and a pair of brackets 41, 41 (an intermediate member 4) having an abutting part 41b to be inserted in the insertion hole 22 and abutted on an inner side face 23 opposite to the insertion hole 22, and a fitting part 42 capable of fitting a cross member 3 (another structure). The abutting part 41b of the bracket 41 is joined to the side frame 2.

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