A front supporting leg rollover protection device of a bridge girder erection machine is characterized by comprising hinge bases and L-shaped rollover protection beams, wherein the hinge bases and the L-shaped rollover protection beams are fixedly connected to the two ends of a front supporting leg upper transverse beam symmetrically, and front supporting leg supporting roller boxes are mounted at the hinge bases at the corresponding ends in a hinged manner; the bottom faces of the two ends of the front supporting leg upper transverse beam are combined with supporting leg inner sleeve columns in a fixed connection manner, and the supporting leg inner sleeve columns are sleeved with the supporting leg outer sleeve columns; a supporting leg lower transverse beam is connected between the two supporting leg outer sleeve columns; each front supporting leg supporting roller box is composed of two supporting roller box bodies, and the two supporting roller box bodies are hinged to a middle connecting beam through hinge pins; a hanging hinge base is welded to the lower face of the middle connecting beam, and the lower face of the hanging hinge base is hinged to a connecting base; and the bottom face of the connecting base is provided with a rollover protection transverse beam in a fixed connection manner, and the rollover protection transverse beam is located below the L-shaped rollover protection beams. In the construction process of hole passing or beam erecting, due to accidental longitudinal force, the front-and-back inclining of a front supporting leg is too large, and the problem of longitudinal overturning of the bridge girder erection machine is solved.