To allow a certain operator to move an operation switch for an operation equipment part operated by the operator closer to the operator side beyond a wing wall simply by opening a plinth board door with a door mechanism, to identify the operation switch as held in his attitude and to easily and quickly operate the operation switch in comfortable attitude.

The operation equipment part operated by the operator is mounted on the back side of a plinth board part with the door mechanism so that the operation equipment part is allowed to be moved integrally with the plinth board part. During non-operation, the operation equipment part is closed and stored on the back side of the plinth board part, and during operation, the operation equipment part can be opened and moved to a cage without contacting the wall face of the cage.