To automatically and accurately adjust the quantity of projection of a holder from a reference member to the reference position at the tip end of the cutting edge.

Based on the photograph information from a camera 15, a turning motor 14 is driven, so that a peripheral corner part of a drill 2 is adjusted to a prescribed rotational phase at which photographing by a picture processing camera can be made properly. Then, an arm 20 is fitted into a nut so as to rotate a holder main body 1, thereby relatively rotating the nut for the adjustment of the position of its end surface. In this way, based on the photograph information of the picture processing camera, the height of the peripheral corner part can be measured, the length from the end surface of the nut to the peripheral corner part of the drill 2 can be adjusted automatically and accurately, the quantity of projection of the cutting edge part can constantly and precisely be kept constant, and a bad influence upon machining can be excluded, thereby promoting man-power saving.