Abstract: In an end mill, eight peripheral cutting edges having a helical shape and a larger outer diameter than that of a shaft portion are in a cutting portion in a circumferential direction. For one peripheral cutting edge of the eight peripheral cutting edges, when a cut length of the peripheral cutting edge along an axial direction is L, a twist angle of the peripheral cutting edge is ?, and a circumferential distance at a lower end of the peripheral cutting edge between the peripheral cutting edge and another peripheral cutting edge adjacent to a tool rotation direction rear side of the peripheral cutting edge is a, n expressed by the following equation is approximately 1 for all of the eight peripheral cutting edges in at least a half region of the cut length from the lower end of the peripheral cutting edge.

Abstract: In an end mill, eight peripheral cutting edges having a helical shape and g a larger outer diameter than that of a shaft portion are in a cutting portion in a circumferential direction. For one peripheral cutting edge of the eight peripheral cutting edges, when a cut length of the peripheral cutting edge along an axial direction is L, a twist angle of the peripheral cutting edge is ?, and a circumferential distance at a lower end of the peripheral cutting edge between the peripheral cutting edge and another peripheral cutting edge adjacent to a tool rotation direction rear side of the peripheral cutting edge is a, n expressed by the following equation is approximately 1 for all of the eight peripheral cutting edges in at least a half region of the cut length from the lower end of the peripheral cutting edge.