PURPOSE: To easily set a reference position at the time of setting the drilling position and angle of an excavating drill relative to an excavated cross sectional area, and realize a practical method suitable for a work site.

CONSTITUTION: First and second sighting targets 26 and 27 are laid on the drill frame 20 of a drilling machine 10 to drill a working face with an excavating drill 23, at the prescribed gap in the advancing and retreating directions of the drill 23, and a beam generator 54 is made to transmit a laser beam 54a toward the working face, in parallel to the working face drilling direction. Furthermore, the first and second sighting targets 26 and 27 on the frame 20 are aligned with the laser beam 54a, thereby indexing and keeping the drill 23 at a reference position in parallel to the working face drilling direction in such a condition as free from rolling and pitching relative to the direction.