To provide a construction method for widening a road passing through a gorge.

A road shoulder slope dropping into a valley from a road is cut out at a substantially right-angle for a road surface to form a foundation natural ground for constructing the road, steel pipe piles 3 are driven into the foundation natural ground at a fixed interval, foundation rubble stones 4 are spread on the cut-out face of the foundation natural ground, and foundation concrete 5 is placed on it. A U-shaped block A having a hole through which a head part 3' of the steel pipe pile 3 passes at the center is placed on the foundation concrete 5, concrete 20 is filled into a clearance between the head part 3' of the steel pipe pile 3 and the U-shaped block A, and lastly, an upper floor slab 10 which becomes the road surface of the expanded road is put on an upper part of the U-shaped block A and is fixed by an anchor bolt 11 implanted in the U-shaped block A.