An apparatus for aligning sheet stacks in a feeder of sheet processing machines includes a motor-driven aligning plate and a movement converter situated between a motor drive and the aligning plate. The movement converter forces a movement describing approximately a circular path onto the aligning plate. A vertical speed component of the aligning plate during aligning corresponds to an upward speed of a feeder stack. A method for aligning sheet stacks in a feeder of a sheet processing machine as well as a sheet processing machine, are also provided.