Claim:
The combination, in a cainera-bed, of a main section; two or more extensible sections adapted to be expanded and retracted with reference to the main section and with reference to each other; operating means for moving said extensible sections longitudinally and successively so as to extend the bed; a lock for automatically connecting said sections to-ether; and means on the main section for automatically releasing said locking device by engagement with said main section when the sections reach a predetermined relative position.