To suppress the degradation of mechanical strength and the worsening of working environment owing to a welding means and to suppress the increase in cost owing to necessary dimensional accuracy in the preprocessing when employing the press-fitting for coupling aluminum parts fitted to each other.

An axle bracket 4 and an under bracket 5 which are aluminum parts are inserted in outer circumferences of outer and inner tubes 2 and 3 of a front fork 1 for two-wheel vehicle which are aluminum tubular parts, the external force is applied to an inner surface side of the outer and inner tubes 2 and 3 in this condition, and the tubes are expanded, and an expanded portion 7 is pressed against inner surfaces of the axle bracket 4 and the under bracket 5 to couple the aluminum parts. As necessary, the coupling is firmer by pushing the axle bracket 4 and the under bracket 5 by a locking portion 8 formed by expanding the expanded portion 7, or pushing the expanded portion 7 into a recess 9 in the axle bracket 4 and the under bracket 5.