a sheet stacker with a separator plate having a movable stacker table with a stack supporter thereon . a first drive means is utilized for alternately lowering the separator plate and the stacker table , and a second drive means is utilized for alternately raising the separator plate and the stacker table . the second drive means is constantly running and two clutches are respectively interposed between the drive means and the plate and table and that second drive means is constantly running and is overcome by the downward drive means , but is effective upon suitable alternate actuation of the two clutches for the plate and the table .