An image forming apparatus which can prevent decrease in useful lives of components for air sheet feeding without bringing about throughput degradation when performing an image forming operation using a plurality of sheet supply units. When a sheet is fed from a first sheet supply unit having a fan that is driven so as to supply sheets, then a sheet is supplied from a second sheet supply unit, and then a sheet is supplied form the first sheet supply unit again, and in a case where a suspension time period over which no sheet is supplied from the first sheet supply unit is longer than a preparation time period from when driving of the fan is started to when the fan is brought into a driving state required to supply a sheet, driving of the fan is temporarily stopped.