To facilitate mounting work in a work machine, perform centering accurately surely, also improve mounting rigidity, in a mounting mechanism for a pin mirror cutter.

In a mounting mechanism for a pin mirror cutter removably mounting a cutter main unit 22 circular annularly shaped to arranged a cutting edge in an internal peripheral part in a cutter mounting part 23 driven to rotate in a work machine, a peripheral part of the cutter main unit 22 is mounted in a fitting condition in an internal peripheral part of a cutter mounting part, a peripheral surface of the cutter main unit 22 and an internal peripheral surface of the cutter mounting part are mutually opposed and brought into surface contact, also formed in a slope gradually diametrically contracting toward the insert direction of the cutter main unit 22 relating to the cutter mounting part, in an internal peripheral surface of the cutter main unit 22, a first tooth 24b arranged with an equal space in a circumferential direction is provided, the cutter mounting part, in its peripheral surface, is provided with a second tooth 25b arranged with an equal space in the circumferential direction to be capable of meshing with the first tooth.