A heat sink preform having a base 2, a fan case engagement portion 3 and a radiating fin formation portion is integrally formed by extrusion molding. A plurality of radiating fins 5 having a tong ratio which is defined as a ration of the height of the radiating fins with respect to the interval dimension between neighboring radiating fins of more than or equal to 10 is formed by subjecting the radiating fin formation portion to cutting work. In this way, a cooling fan attached type heat sink with a plurality of radiating fins having a shape that is difficult to be formed or cannot be formed or having a large tong ratio can be produced with low costs and with relative ease.