A ball end mill includes an end mill body having an axis of rotation therethrough and an indexable cutter insert releasably attached to a forward end portion of the body. The insert includes a plate having front and rear faces. The front face has at least one generally arcuate first marginal ridge with the first marginal ridge serving as a respective generally arcuate main cutting edge. The front face has at least one short second marginal ridge with the second marginal ridge serving as a respective short cutting edge. The main cutting edge has a leading end portion disposed at one end thereof and intersecting the short cutting edge in such a manner that an angle defined by the leading end portion and the short cutting edge is obtuse. The front face serves as a rake surface for the cutting edges and has a marginal surface portion disposed adjacent to the short cutting edge and the leading end portion. The marginal surface portion is convexly curved so as to slope toward the rear face toward the short cutting edge. The arrangement of the first insert with respect to the body is such that the leading end portion of the main cutting edge is disposed adjacent to the axis of the body, and that the short cutting edge extends from the leading end portion beyond the axis of the body toward the rearward end portion of the body when viewed in a direction generally perpendicular to the front face.