To provide a milling device in which a cutter main body can be installed solidly without generating a play, as well as the cutter main body can be installed simply.

A second adaptor 20 provided with a through hole 21 for rotary member at the center, and plural through holes 22 for holding member at the periphery, is installed to form a space 23 between a first adaptor 10 which is installed to the front end surface of a main shaft spindle, and a rotary member 30 is housed to expose its tip end face in a central part of the space 23 through the through hole to the center part so as to be held to the second adapter 26. At the same time, the screw part 31 of the rotary member, and the screw hole 41 of at the center part of an elevation member are engaged to house the elevation member in the space, plural holding parts 50 are projected on the front end side through the through holes at the periphery provided to the second adapter, and a ring form cutter main body 60 is locked to the locking parts 51 at the front ends of the holding members 50.