To facilitate handrail installation and formwork for placing concrete for a support wall body (vertical structure) in a PCa staircase which is for use as a safe and broad work passage prior to construction of a skeleton.

The PCa staircase basic material 1 includes a stepped staircase portion 6, has an axially extending support steel product 13 embedded therein, and then has installation steel plates 17, 18 attached thereto, for covering both inner and outer side surfaces. An installation hole 23 is bored in the outer installation steel plate 18. Further, a protrusion 14 of the support steel product 13 and a protrusion 56 of an anchor bar 55 are formed on an external surface of the inner installation steel plate 17, which are formed as the PCa staircase 30 and the like. By arranging the PCa staircase 30 and the like prior to construction of the skeleton, temporarily fixing the same to a preliminary temporary support column 40, and fixing the projection 14 to a preliminary structural column 38 (support wall body 36), the PCa staircase 30 and the like can be erected alone, to thereby function as the work passage. Concrete is placed by using the installation steel plate 17 as part of a form, and then the projection 56 is embedded in the support wall body 36, whereby the PCa staircase 30 and the like can be installed with sufficient strength. Then, the PCa handrail 50 is installed into the installation hole 23 by means of bolts.