To make it possible to easily put a mark on a wall material using a box detector, and position a drilling tool at the mark with accuracy so that a hole can be drilled at the exact position in the wall material.

A box detector 4 contains a guiding section 41 for guiding a pen or pencil 40 in order to draw a mark 61 analogous to the outline of a wiring box. The box detector 4 is stopped in a position where a wiring box is detected, and a mark 61 analogous to the outline of the wiring box is drawn on the surface of a wall material 37 along the guiding section 41. Thereafter, a drilling tool 1 having an aligning section 42 the outline of which is analogous to the outline of the wiring box is aligned with the mark 61 on the wall material 37, and in the state a hole is drilled in the wall material 37.