To make optimum arrangement of a movable structure in a step floor shape used at seat facilities or stage equipment in a theater or a ball for an event by actually increasing the degree of freedom as layout variable facilities without sacrificing storage capability when it is not used.

A step floor 1 is split into right and left structural parts 3 at the split face 2 shifted at equal spaces step by step in a plane view for the step-by-step split parts to be in geometrically analogous shape, so that it can be changed into planely various shapes by shifting the combination of the split parts, as required. The shift in elevation of the step floor arising when the combination is shifted can be adjusted by an elevator provided for either or both of the split structural parts 3, 4.