PURPOSE: To drill many holes at the bottom of a vertical hole by installing a drilling device having a drifter elevated along a holder which is supported on a rotary table and horizontally turned in the center of the vertical hole.

CONSTITUTION: A frame main body 4 of a vertical hole drilling device 2 is installed substantially in the center of a vertical hole 1 and controlled to be horizontal. An expansion arm 5 is elongated, and the tip of a support arm 9 is brought into contact with a liner plate 10 of the periphery of the vertical hole and fixed. Subsequently, after the inclination angle and height of a holder 18 and a guide cell 21 are adjusted, a boom 15 is moved in the horizontal direction by a boom retreating motor 16 to shift a drifter 24 to a drilling position, and compressed air is supplied to drill the bottom of the vertical hole 1 by striking and rotation of a bit 26. Further, a feeding motor 27 is driven to descend the drifter 24, thereby drilling to a designated depth. After the completion of drilling to a predetermined depth, the feeding motor 27 is reversed to lift up the drifter 24, a rotary table 12 is rotated to move the boom 15, and the bit 26 is moved to the next drilling position to perform drilling.