PURPOSE: To share a unit without generating a clearance and an interference at the time of connection.

CONSTITUTION: In staircase structure, in which stepped sections 12 and the end connection sections 13a of a staircase unit having handrail sections 17, 17 on both sides of the stepped sections 12 are connected at the end connection sections 14a of stair landing units 14, size B among both external surfaces in the end connection sections 13a of the handrail sections 17 is set in values narrower than size C among both external surfaces of the end connection sections 14a of the stair landing sections 14. The stair landing unit 14 has a stair landing 31 in a square, and handrails 32 are disposed on one adjacent two side faces in the four side faces of the stair landings 31 while staircase units 13, 16 or the end connection sections 14a connecting other stair landing units 14 are mounted on the other adjacent two side faces.