To bore a hole in a desired position precisely and easily by furnishing a guide rod on its one surface with a rotary plate rotatably along one of surfaces over two positions, the position accommodated in the surface and the other where the tip is protruding from the surface.

A hole 16 is bored in a vertical panel 11 to be joined with a transverse panel 10 in the position mating with a hole 15 provided in the transverse panel 10, which is carried out in the condition that that surface of a guide rod 22 provided with a through hole 28 is contacted with that part of an inside surface of the panel 11 which is to be bored. Then a rotary plate 30 is turned so that its reference surface is contacted with the end face of the panel 11, and a jig 20 is located by putting a mating reference surface 24a of a backing plate 24 in contact with the end face perpendicularly intersecting the end face where the reference surface is in contact. The jig 20 is secured by a clamp to the panel 11, and a hole 16 is formed by inserting an boring drill into the same through hole 28 as the hole 15 provided in the panel 10. Thereby boring 16 can be made precisely, in the mating positions on the panels 10 and 11.