To rapidly construct a concrete staircase by eliminating the need for forming a rough finished concrete staircase in advance, and simplifying construction processes.

A stepped cutout 40 is formed in a side form panel 4 fixed to each side of a slab panel S. The cutout 40 has a horizontal side portion 41 and a vertical side portion 42. A riser fixture 2a is fixed near the vertical side portion 42. A riser 1 rests between lifting elements 21. Each end of the riser 1 is brought in outwards through the cutout 40 of the side form panel 4. The left upper surface portion 11 of the riser 1 is made to directly abut the end of the horizontal side portion 41 of the cutout 40 and the right upper surface portion 11 of the riser is made to indirectly abut the end of the horizontal side portion 41 of the cutout 40 via a spacer 6, so that the riser 1 is sandwiched in place between the lifting element 21 and the horizontal side portion 41 of the cutout 40.