An image forming apparatus comprising a tray for receiving sheets with an image, which is movable up toward and down away from a sheet ejection portion of a transport path, the tray being moved down intermittently in accordance with the volume of sheets stacked thereon. When a signal commanding an image forming operation is generated, the tray is moved to a proper position, where the upper surface of the tray or the upper surface of sheets stacked thereon is positioned below the sheet ejection portion with a specified space, and during the movement of the tray, the image forming operation is kept standing by. The tray is moved to the proper position when the volume of the sheet stack is varied during the image forming operation. The transport path for leading sheets ejected from a copying machine to the tray comprises a first transport section for ejecting sheets onto the tray and a second transport section arranged upstream of the first transport section, and when a sheet is about to be ejected to the tray, the travel speed of the sheet is reduced from a first speed to a second speed. When the next sheet comes into the second transport section during the transportation of the former sheet in the first transport section at the second speed, the travel speed of the former sheet in the first transport section is returned to the first speed.