PURPOSE: To easily correct any boring dislocation with a check mark without leaving this mark behind on a final product by installing plural pieces of the dimensionally different check marks for positioning at the time of secondary working, in at least two spots on diagonal positions other than a part serving as a final product where circuits are formed.

CONSTITUTION: Boring is performed by a boring tool in positions corresponding to check marks 3 of a work 1 provided with plural pieces of these dimensionally different check marks 3 in at least two spots on diagonal positions other than a part 2 serving as a final product where circuits are formed. At this time, a positional slippage of the work against the boring tool is judged by a positional relationship between the hole and the check mark 3, and the work 1 is positioned so as to make the slippage become within the specified value.