To improve the working efficiency by connecting a screw and a rod to each other, and setting a total of the connection length to a depth of a target excavation hole or more.

A leader 4 is stood on the ground, and a screw head 10a provided at a tip of a screw 10 is positioned at an excavation position, and a motor 5 is driven so as to rotate the screw 10. The screw 10 goes ahead while discharging the earth, and when the whole length of the screw 10 is embedded in the ground, the screw 10 is drawn up once. Excavation at the second time is started, and the excavation is continued by the whole length of the screw 10. Each time when the whole length of the screw 10 is embedded in the ground, the screw is drawn up, and the similar excavation is repeated several times so as to form an excavation hole having a target depth. In this case, in the case where length of the screw 10 is short, quantity of the mud or the like to be pulled up at one time is small, and quantity of the mud to be fallen onto a bottom of the hole is small, and the hole having the accurate depth can be excavated. Efficient excavation can be performed in the case of using this device for a pile placing machine requiring accuracy of excavation hole.