Ball end mill and cutting insert

A ball end mill comprising

• a ball end cutting edge on a distal end in an axis line direction, a rotation locus of the ball end cutting edge around the axis line being formed in an approximately hemispherical shape,
• wherein the ball end cutting edge includes a large diameter edge, and the large diameter edge is formed in an arc shape having a curvature radius larger than a ball radius of the ball end cutting edge,
• a plurality of the large diameter edges are formed in a region 80% or more to 120% or less of the ball radius from a center of the ball end cutting edge from a distal end to an outer peripheral end of the ball end cutting edge,
• the plurality of large diameter edges each have an identical cutting width in a predetermined region from the distal end to the outer peripheral end side of the ball end cutting edge,
• the plurality of large diameter edges each have the identical curvature radius, and
• when an imaginary circle having the ball radius is drawn with the center of the ball end cutting edge as a center, the imaginary circle internally contacts respective rotation loci of the plurality of large diameter edges;
• wherein the ball end cutting edge includes a plurality of small diameter edges, and the plurality of small diameter edges connect between the large diameter edges and have arc shapes having curvature radii smaller than the ball radius, and
• the large diameter edges have cutting widths larger than cutting widths of the small diameter edges.