Abstract: An apparatus for straightening stacks of sheet material which includes a base on which there is rotatably mounted a device for supporting a stack of disposed sheets in an initial horizontal position and a position in which the stack is resting on a support with the sheets in vertical position, a vibrator for straightening the vertically disposed sheets against the support and against a stacking strip, and lifting bars for raising the vertical sheets from a first position below the support to a position above the support plane and back to the first position.