To provide a method for producing a large-sized heat sink of an optional size in a good condition.

A heat sink 1 is produced by joining a plurality of extruded shape materials 10, each of which has a shape such that a plurality of plate fins 12 are projected at right angles and parallel to the one face of a base plate 11. The production method is characterized by making one edge face 13 of the base plate 11 of the plurality of extruded shape materials 10 parallel to the plate fins 12 abut on the same face of the adjacent base plate before an oxide film is generated on the material 10, and then welding the resultant abutting part 20 from the side face opposite to the plate fins 12 by a direct current straight polarity TIG welding method.