Variable lead end mill

A variable lead end mill having a plurality of peripheral cutting edges with different helix angles,

• the variable lead end mill having a flute bottom diameter of a plurality of helix flutes making up rake faces of the plurality of the peripheral cutting edges, the flute bottom diameter increasing in an axial direction from a tool tip toward a shank, and
• a cross-sectional shape of the helix flute orthogonal to an axial center on a cutting-edge rear side leading to a heel of a land of the peripheral cutting edge being defined based on a tangential line drawn from the heel of the land to a flute bottom circle passing though flute bottoms of the plurality of the helix flutes such that a flute wall surface falls within an allowable range defined with a width dimension of 0.05 D on each of both sides of the tangential line wherein D is a cutting diameter of the variable lead end mill.