A sheet supply device includes a sheet supply tray, a delivery roller contacting a topmost surface of a sheet bundle on the sheet supply tray to deliver the sheet, and separation means feeding the sheet delivered by the delivery roller one by one in a separated manner. The sheet supply device further includes an elevating tray freely elevated/lowered to support a leading end side of the sheet bundle placed on the sheet supply tray and to move the topmost surface of the sheet bundle to a delivery position, a first drive section elevating/lowering the elevating tray, a second drive section elevating/lowering the delivery roller, and a controller controlling the first and second drive sections to elevate the elevating tray until the topmost surface of the sheet bundle reaches the delivery position and thereafter lower the delivery roller to a position contacting the topmost surface of the sheet bundle.