Abstract: Apparatus for changing the orientation of successive stacks of overlapping paper sheets has a first conveyor which delivers stacks seriatim onto the upper side of a support located below a vertically movable and rotatable turntable having at its underside a layer consisting of rubber and formed with openings for escape of air. The support has plenum chambers which discharge streams of compressed air against the underside of a stack between the support and the turntable whereby the stack is lifted off the support and bears against the layer at the underside of the turntable before the latter begins to rotate through 90 degrees to thus change the orientation of the stack. Prior to rotating, the turntable is moved downwardly toward and bears against the stack on the support to thereby expel air from the stack and to cause opening of valves in the upper side of the support by way of the lowermost sheet of the stack.