To provide a construction method which enables even a low-skill worker to more rapidly and more easily construct a tread of a steel-frame staircase than when adopting a conventional construction method.

This construction method for making the tread of the steel-frame staircase by poring mortar into a steel frame is characterized in that the height of a tread board having a groove preprovided on its backside is adjusted by using at least four sets of λ-type height adjusting implements and base metal frames which enable the selection of a position to adjust a mounting height.