Abstract: A cooler for cooling hot bulk material, in which cooling gas flows transversely to the conveying direction through a bulk material bed cooling the bulk material. An apparatus carrying the bulk material bed has a ventilation floor comprised of movable planks extending in the conveying direction through which cooling gas flows. At least two adjacent planks are moved simultaneously in the conveying direction and non-simultaneously counter to the conveying direction. The planks have differently configured surfaces, on which the bulk material bed lies, in the conveying direction, and these surfaces, due to different frictional locking with the bulk material bed lying thereon, lead to differing mean transport speeds, and as a result the bulk material bed is stretched in a region of quicker conveying and compressed in a region of slower conveying. The apparatus tumbles the bulk material with vertical mixing, thereby heat is recuperated efficiently.