A ball nose end mill includes a tool body and a throwaway insert mountable on the tool body. The throwaway insert includes a bottom face as a mounting face, an upper face on an opposite side from the bottom face, a side face formed between the bottom face and the upper face, and a cutting edge formed along an intersecting ridge between the upper face and the side face in a substantially arc shape such that the rotational trace of the cutting edge when the throwaway insert is attached to the tool body in use substantially forms a partial spherical surface. An undulating portion, which is formed by alternately arranged concave portions and convex portions, is provided on the upper face so as to intersect the cutting edge. At least one of the concave portions is formed as a deep-concave portion which has a greater depth than that of the others.