Subsurface exploration on the Moon is a significant mission for future space developments. The authors have studied an autonomous robotic explorer which can burrow into the soils. This paper focuses especially on the excavation mechanism of a burrowing robot for near-future lunar subsurface exploration. The main objective of the proposed robot is to bury a scientific observation instrument, such as a long-term seismometer under the lunar surface, which is covered with very compacted lunar regolith. Therefore, an efficient drilling mechanism is required. In this paper, the authors propose a non-reaction screw drilling mechanism with double rotation, which is called the contra-rotor screw. This paper also evaluates the feasibility and effectiveness of the proposal of a burrowing robotic system through some experimental analyses.