An excavation machine having a cutter head with a large diameter while making it possible to excavate excavation objects such as hard bedrock etc. with high efficiency is provided. The excavation machine comprises an outer circumference cutter head 20 having a circular opening and being rotated and contacted to excavation objects and a small diameter cutter head 23 disposed in the opening and rotatable independently from the outer circumference cutter head. Rotation centers of the rotation disk and the rotation plate are gapped and the gap is shorter than a rotation radius of the small diameter cutter head.