Reusing method of end mill

A reusing method of an end mill comprising a columnar shank part and a cutting part integrated with the shank part, wherein

• the end mill has a margin which is a part of a circle having a diameter identical to a diameter of the shank part, the margin being provided on an outer edge of the cutting part in cross-section orthogonal to an axial direction;
• a base material of the end mill is machined in advance so as to have coaxiality having equal accuracy to coaxiality for the cutting part;
• the shank part is an unmachined part left without cutting the base material;
• the margin is a part of an outer peripheral surface of the base material left without cutting the base material when the outer edge is formed by cutting the base material;
• and
• when the cutting part is worn out, the cutting part is cut off and a new cutting part is machined on the shank part while a part of the outer peripheral surface of the shank part is left as the margin without cutting and without additional machining for ensuring formation of a new outer peripheral surface and accuracy of coaxiality, the new cutting part having a shape, accuracy of coaxiality, and an outer diameter identical to the shape, the accuracy of coaxiality, and the outer diameter of the cut-off cutting part, and in a plurality of re-manufacture processes, cutting parts newly machined one after another have a shape, accuracy of coaxiality, and an outer diameter identical to the shape, the accuracy of coaxiality, and the outer diameter of the original cutting part.