REAMER

PROBLEM TO BE SOLVED: To provide a reamer in which width of a margin is secured to improve machining precision and cutting resistance can be reduced.SOLUTION: The reamer 10 has an edge part 20 on an outer periphery thereof. The edge part 20 includes first cutting edges 25, 26 having a margin 23 continued from the cutting edge 21, and second cutting edges 35, 36 having a margin 33 width B of which is broader than width A of the margin 23 of the first cutting edge 25, 26. The second cutting edge 35 is arranged next to the first cutting edge 25. The second central angle 2 formed by the second cutting edge 35 and the next first cutting edge 26 is set smaller than a first central angle 1 formed by the first cutting edge 25 and the next second cutting edge 35 along a rotating direction. The tip end of the second cutting edge 35 is retreated to a shank side of a tip end of the first cutting edge 25. The width of the margin is secured to improve the machining accuracy and the cutting resistance can be reduced.