To shorten machining time when machining a deep hole on a machining surface of workpiece, and to improve accuracy of the deep hole.

After making a bush 102 of a guide member 76 abut on the machining surface 122 for machining the deep hole of the workpiece 16, a drill 74 is inserted in the bush 102 made from super hard material. Thereby, a pair of guide portions 89a, 89b formed on an outer peripheral surface of the drill 74 holds the drill 74 in an axial direction by the bush 102. Therefore, the drill 74 rotating under driving action of a rotation driving source is displaced toward the workpiece 16, thereby forming the deep hole 17 with predetermined depth on the workpiece 16 through the guide member 76 abutting on the workpiece 16.