To provide an erection method capable of erecting girders by the interruption of the traffic within a short time without using any large-scaled crane in a narrow building site unable to ensure a wide construction working zone.

In the method erecting the girders 2 across the road on the existing roads 1 and 1', built-up yards 6 are installed along the existing roads from an erection point (a) to assemble the girders 2 on either one side of two points (a) and (b) erecting the girders across the existing roads, and the assembled girders are horizontally turned along a side track 8 erected over the front end sides of the built-up yards and in the vicinity of the erection point (b) on the opposite side to erect the girders over between both points.