A sheet feeding apparatus including sheet feeding unit; a pressure plate on which sheets are stacked and which is biased so that an uppermost sheet of the stacked sheets comes in pressure contact with the sheet feeding unit; a first pressing-down mechanism which presses down the pressure plate to separate the uppermost sheet and the sheet feeding unit by a constant distance when the sheet feeding unit is not operated; a second pressing-down mechanism which is adopted to press down the pressure plate when an amount of the sheets stacked on the pressure plate is smaller than a predetermined amount, and is given a load from the pressure plate depending on a position of the pressure plate; and sheet stacking amount detecting unit which measures the load and detects a stacking amount of the sheets stacked on the pressure plate on the basis of the measured load.