A sheet feeding apparatus comprising: a sheet stacker on which a plurality of sheets are stacked; an air blower configured to blow air from a lateral side of the plurality of sheets stacked on the sheet stacker to the plurality of sheets to float an uppermost sheet of the plurality of sheets; a suction feeder disposed above the sheet stacker and configured to suck the uppermost sheet floated by the air blower and feed the sheet in a feed direction; a lifting mechanism configured to lift the sheet stacker; an elevation detection sensor configured to detect that the plurality of sheets stacked on the sheet stacker has reached a detection position located above the sheet stacker and below the suction feeder; a feed detection sensor configured to detect the sheet fed by the suction feeder; and a controller configured to control operations of the air blower, the suction feeder, and the lifting mechanism based on detection results of the elevation detection sensor and the feed detection sensor, characterized in that the controller is configured to: drive the lifting mechanism such that the sheet stacker is lifted by an elevation amount determined based on a sheet thickness (t) of the sheets stacked on the sheet stacker, each time a sheet is detected by the feed detection sensor when a number of sheets detected by the feed detection sensor is smaller than a threshold number of sheets; and stop lifting of the sheet stacker until a sheet is not detected by the elevation detection sensor when the number of sheets reaches the threshold number of sheets, while repeatedly performing processing to feed the uppermost sheet floated by the air blower to the suction feeder and count the number of sheets detected by the feed detection sensor. a sheet stacker on which a plurality of sheets are stacked; an air blower configured to blow air from a lateral side of the plurality of sheets stacked on the sheet stacker to the plurality of sheets to float an uppermost sheet of the plurality of sheets; a suction feeder disposed above the sheet stacker and configured to suck the uppermost sheet floated by the air blower and feed the sheet in a feed direction; a lifting mechanism configured to lift the sheet stacker; an elevation detection sensor configured to detect that the plurality of sheets stacked on the sheet stacker has reached a detection position located above the sheet stacker and below the suction feeder; a feed detection sensor configured to detect the sheet fed by the suction feeder; and a controller configured to control operations of the air blower, the suction feeder, and the lifting mechanism based on detection results of the elevation detection sensor and the feed detection sensor, characterized in that the controller is configured to: drive the lifting mechanism such that the sheet stacker is lifted by an elevation amount determined based on a sheet thickness (t) of the sheets stacked on the sheet stacker, each time a sheet is detected by the feed detection sensor when a number of sheets detected by the feed detection sensor is smaller than a threshold number of sheets; and stop lifting of the sheet stacker until a sheet is not detected by the elevation detection sensor when the number of sheets reaches the threshold number of sheets, while repeatedly performing processing to feed the uppermost sheet floated by the air blower to the suction feeder and count the number of sheets detected by the feed detection sensor. drive the lifting mechanism such that the sheet stacker is lifted by an elevation amount determined based on a sheet thickness (t) of the sheets stacked on the sheet stacker, each time a sheet is detected by the feed detection sensor when a number of sheets detected by the feed detection sensor is smaller than a threshold number of sheets; and stop lifting of the sheet stacker until a sheet is not detected by the elevation detection sensor when the number of sheets reaches the threshold number of sheets, while repeatedly performing processing to feed the uppermost sheet floated by the air blower to the suction feeder and count the number of sheets detected by the feed detection sensor.