PROBLEM TO BE SOLVED: To enhance excavating efficiency by setting at least one-end side excavating rod, of a plurality of excavating rods of a multi-shaft type excavator, so that the tip position is situated substantially above the tip positions of the other excavating rods. SOLUTION: When motors 54A, 54B are rotated, excavating rods 34B, 34D are rotated in the same direction, and excavating rods 34A, 34C, 34E are rotated in the opposite direction. When an excavating rod assembly 34 is then lowered, the auger heads 40B-40D of the excavating rods 34B-34D start to excavate a shaft. The auger heads 40A, 40E of the excavating rods 34A, 34E shorter than the excavating rods 34B-34D by 1m or more start to excavate the shaft. When the first excavation is ended, excavation is started in a position distant from the shaft by the excavating rods 34B-34D by a prescribed distance. Thus, since it is not required to perfectly overlap one shaft with the previous shaft every excavation cycle, the excavating efficiency can be enhanced.