To provide a boarding bridge in which a passage width can be expanded and rain water can be drained well.

A water cutoff member is installed for preventing water from entering the right and left lower parts in the axial direction of an inner tunnel having a telescopic structure at the telescopic type tunnel. A gutter pan for an outer tunnel is arranged below the water cutoff member to cause a width of the gutter pan to be narrow and correspondingly the passage width of the outer tunnel is widened. Rain water flowing down at a side wall of the inner tunnel is transmitted along the water cutoff member of reinforcing member arranged at the lower side of the side wall and flows down into the lower gutter pan. With this configuration, the water is prevented from flowing into the inner part along the surface of the reinforcing member and it becomes possible to make a narrow width of the gutter pan installed at the outer tunnel member.