To promote the improvement of processing accuracy and the shortening of working time while assembling easily and also securing working safety at a site.

This processing device 1 for removing a bolt by counterboring is assembled at the site by fixing a table holding jig 5 and a fixing jig 6 to a fixing bolt 15 except the bolt 15 to be worked on a flange 13 after their positioning is made to the flange face 14 of the flange 13 on which the bolt 15 to be worked is mounted, by fixing a X-Y table 4 on which a column 3 is mounted to the table holding jig 5, and by fixing a drill device 2 to a slide head 7 of the column 3. After the processing device 1 for removing the bolt by counterboring is assembled, the drill tip of the drill device 2 is made the positioning to the central position of the bolt 15 to be worked by moving the X-Y table 15.