PURPOSE: To use stairs as an elevator if necessary by providing mechanism for lowering an upstairs floor plate and step boards from a normal stair position into a fixed position near the height of a downstairs floor face and returning the upstairs floor plate and step boards upward into the stair position to hold them into the respective positions.

CONSTITUTION: A pair of drive screws 4a in automatic elevating drive mechanism 4 are rotatory-driven to lower an upstairs floor plate 1 and step boards 2 respectively from a stair position to a fixed position near the height of a downstairs floor face F1 and to hold the floor plate 1 and step boards 2 into this position in an almost flat state. As a result, a wheelchair can advance on the step boards 2 to get on the upstairs floor plate 1. A pair of drive screws 4a in the drive mechanism 4 are then reversely rotated to return the upstairs floor plate 1 and step boards 2 upward into the stair position and to hold them into this position. As a result, the wheelchair can reach upstairs along with the upstairs floor plate 1 and go out to an upstairs corridor.