A platform 12 is supported by four belts 22 to 25. Of the belts 22 to 25, a pair of belts 24, 25 is attached to a pivoting arm 26 so that the pivoting arm 26 is pivotable around a pivoting shaft 28. Pivoting of the pivoting arm 26 absorbs, for example, the difference in length between the belts 24, 25. The present invention makes it possible to simplify an elevate and lower driving mechanism of the platform 12 and to easily adjust the lengths of the belts 22 to 25. The present invention also makes it possible to prevent vibration during elevation or lowering and to allow the belts 22 to 25 to stand long use.