A plurality of chip discharge flutes are located on an outer periphery of a tip portion of the end mill body which rotates on its axis. Helix angles between the axis and the cutting edges in the chip discharge flutes, of which are at least one or more; are different from others. A cross-section perpendicular to the axis shows that a flute bottom face in a main flute portion forms a concavely curved shape from the rake face to a point where the flute bottom face, touches a web thickness circle of the end mill body, forms a linear shape, and goes toward the end mill rotating direction; and a flute bottom face in a sub-flute portion forms a linear shape, intersects with the flute bottom face in the main flute portion at an obtuse angle, goes further toward the end mill rotating direction.