A sheet feeding apparatus and an image forming apparatus which can reliably feed even sheets having a non-uniform thickness to prevent excessive stacking.An auxiliary tray 1 is swingably provided on the upper surface of a tray 2 which is provided in a cassette body 3a to be lifted and lowered and stacks sheets thereon. When the sheets are stacked, a swing regulating portion 12 regulates the swing of the auxiliary tray 1 when the tray 2 is in a sheet stacking position and releases the regulation of the swing of the auxiliary tray 1 when the tray 2 is lifted.