SHEET FEEDER AND IMAGE FORMING APPARATUS

There is provided a sheet feeder including: a lifting unit that lifts a loading portion having a recording medium loaded thereon; a position detecting unit that detects whether the uppermost surface of the recording medium is disposed at a predetermined first position; a sheet feed mechanism that feeds the recording medium from the loading portion; a thickness detecting unit that detects thickness of the recording medium fed by the sheet feeding mechanism; and a control unit that, when the position detecting unit detects that the uppermost surface of the recording medium is disposed at the first position, controls the lifting unit such that the uppermost surface of the recording medium is lifted up to a second position that is higher than the first position by a distance determined based on cumulative value of the thickness of the recording medium detected by the thickness detecting unit.