Abstract: Sheet feeding apparatus, particularly for feeding corrugated paperboard sheets to container blank processing machinery, has an indexing transmission for cyclically accelerating and decelerating belts or the like for frictionally engaging and feeding sheets from an end of a stack of sheets. A cam arrangement cyclically shifts the feed belts or the like relative to a stack support surface between an operative position for feeding and an inoperative position. The accelerating and decelerating cycle of the belts occurs twice per machine cycle. The cam arrangement preferably comprises a single lobe cam and a double lobe cam, either of which can be selectively chosen for shifting the belts. When feeding one sheet per machine cycle of the downstream machinery, the single lobe cam is employed to shift the belts into the operative mode only once per machine cycle.