An analysis was made of the effect of the advance of tunnel boring machine (TBM) for constructing double railway tracks under an existing another shield driven tunnel of NTT (Nippon Telegraph and Telephone Corporation) with a clearance of approximately 3 m. The convergence of the NTT tunnel and displacement of the ground transverse to the tunnel were measured using the reflection of laser beam from the target in the fiber optic cable laid in the tunnel. To determine the effect of tunneling in the vicinity of the NTT tunnel by advancing a shield across the NTT tunnel, changes in resultant stress in the NTT tunnel were calculated