Abstract: A throwaway ball end mill comprising an end mill body and a tip pressed by a clamp screw onto a cutout formed at the forward end of the end mill body. The cutout is formed in a longitudinal direction with respect to the end mill body, and a pair of lateral regions forked by the cutout have opposite flat surfaces, the lateral regions have clamp holes formed in a direction making a right angle with the cutout, one clamp hole has a conical surface extending toward the periphery of the corresponding lateral region, and the other clamp hole has a female thread formed therein,the centerline of the conical surface is deviated from that of the clamp holes toward the base end of the end mill body. When the clamp screw is tightened with the tip inserted in the cutout, the tip is pressed against the end of the cutout accordingly, and at the same time one lateral region is bent toward the other lateral region.