PURPOSE: To easily execute a bending work without deforming a heat sink fin by disposing the fins at an interval, inserting a metal pipe into the pipe insertion hole of the fin, enlarging the diameter of the pipe of bent inner row, and then bending the whole in a L-shape.

CONSTITUTION: A plurality of heat sink fins 10 are aligned linearly at a predetermined interval by an arraying jig. U-shaped metal pipes 20A-20F having slightly smaller diameter than that of pipe insertion holes 11A-11L of two vertical rows and 6 lateral stages provided on the fins 10 into the holes 11A-11L. Then, a pipe diameter enlarging jig is inserted from the open ends of the pipes 20A-20C of the bent inner row to enlarge the diameters of the pipes 20A-20C. Thus, the fins 10 are secured with the pipes 20A-20C. The whole is removed from the arraying jig, and bent in L shape together with the pipes 20A-20F by a bending press. The open ends of the pipes are formed totally with five U-shaped pipes 40.