A heatsink of the present invention has a column having a heat conducting plate with a heat receiving face contacting a heat producing element. On the side faces of the column are a plurality of first slits disposed parallel to the heat receiving face and a plurality of second slits disposed transversely to the heat receiving face. These slits form a plurality of pillar-type protrusions functioning as fins for cooling. At least one of cross sections of the column has a shape of a rectangle, a trapezoid, a triangle or a shape which tapers off as it goes away at right angle from the heat receiving face. A method of manufacturing the heatsink of the present invention includes first and second processes. In the first process, the first slits are formed by providing a plurality of metallic plate fins on the column along its length by the methods including the extrusion molding using a metallic mold. In the second process, the second slits are formed in a direction approximately transverse to the length direction of the plate fins. By using a specialized jig for the machining of the second slits, many fins can be formed remarkably efficiently. A cooling apparatus for the present invention includes a cooling means mounted on the heatsink of the present invention. The cooling apparatus for the present invention enjoys a high cooling capability and reduced size.