PURPOSE: To remove a drive chain without lowering a lift base to the lowest position during the maintenance of the lift base.

CONSTITUTION: A drive sprocket 16 is fixed at the center section of a drive shaft 15, and an intermediate sprocket 17 is fixed at the end section of the drive shaft 15. A suspension chain 14 for lifting or lowering a lift base is engaged with the drive sprocket 16. A drive chain 25 is wound on the intermediate sprocket 17 and a motor sprocket 24 provided on the output shaft 23 of a drive motor 22. A fixing bolt 31 is inserted into an insertion hole 32 formed on the intermediate sprocket 17, and it is screwed into a screw hole 34 formed on a bracket 33 on the main body 11 side. The intermediate sprocket 17 is made unrotatable, the suspension chain 16 is made unmovable, and the drive chain 25 can be removed.