To provide a method capable of manufacturing a ferrule having through holes high in roundness and small in dispersion and lowering manufacturing cost.

This inside diameter machining device of a cylindrical body 15 having the through holes in the longitudinal direction is furnished with a fixing part 10 to fix the cylindrical body in a state where a plurality of the through holes are arranged to continue, a machining part 30 to polish the cylindrical body by inserting a wire 31 through each of the through holes and sliding it back and forth in the axial direction and a rotating part 20 to rotate a plurality of the cylindrical bodies around its shaft as a center, and the fixing part pressurizes and fixes both ends of a plurality of the cylindrical bodies by a spring 11.