PURPOSE: To provide a drilling device which can drill safely in the direction other than in the square direction to the surface of a drilling object, by providing a guide rod, a device main body having a cutter for drilling, and a reaction means.

CONSTITUTION: A pair of the left side and the right side link mechanisms 4 and 4 are provided to a reaction means H, the fixing position of a regulation link 7 is regulated by utilizing the slits 5a and 6a of the first link 5 and the second like 6, the angle formed by the links 5 and 6 is regulated almost continuously, the angle is made corresponding to the inclination angle of a concrete mat M, and a constantly horizontal drain hole is formed. Then one end of an anchor bolt 12 is fixed to a concreted anchor 16, a pedestal plate 10 is inserted to the other end of the bolt 12, so as to set the link mechanisms 4, and the other end of the bolt 12 is inserted to the slit of a reaction plate 11 so as to regulate the installing position of the reaction plate 11 to the plate 10, and after that, the link mechanisms 4 are fixed by fastening with a fixing nut 13, and the drilling is carried out by rotating a cutter 1.