The utility model relates to a bridge erecting machine capable of erecting double-track twin beams at a tunnel entrance by zero distance. A rear support leg (1) of the bridge erecting machine is supported at the rear end of a longitudinal guide beam and connected with the longitudinal guide beam through bolts, a beam crane I (4) and a beam crane II (5) run on double tracks of the longitudinal guide beam by the aid of a longitudinal moving crane (4-2), an auxiliary support leg (6) runs on a bottom plate of the longitudinal guide beam through suspended rollers (6-1), a middle support leg (7) runs on the bottom plate of the longitudinal guide beam through suspended rollers (7-1), and a front support leg (8) is fixed to the front end of the longitudinal guide beam through bolts. The heights of the longitudinal guide beam and all the support legs are reduced, so that the requirement of the integral bridge erecting machine passing a tunnel is met. By adopting a U-beam structure, the heights of the beam cranes are reduced, so that the requirement of in-place transverse motion during beam erection by transversely moving the cranes is met. The clearance between the bottom face of the longitudinal guide beam and the upper surface of a girder is guaranteed, thereby accommodating transverse motion of a hoisted beam during beam erection. Adoption of the four support leg sets guarantees that support points reach pier positions during variable-span beam erection, so that stress condition of the beams is fine, and the condition of erecting the double-track twin beams at the tunnel entrance by zero distance is met.