A sheet separating device includes: an air blowing unit that is configured to blow air toward a side face of stacked sheets being stacked with a plurality of sheets to separate the sheets by forming an air layer between the sheets; and a sheet pressing unit that is configured to apply a pressing force on the uppermost sheet in the stacked sheets while the uppermost sheet is separated from other sheets, the pressing force having a downward component and a component in a direction along the uppermost sheet.