An image forming apparatus has an image forming device, a first discharge tray for receiving a sheet on which an image was formed, a conveyer for selectively transporting the sheet on which the image was formed by the image forming device to one of a first discharge tray and a sheet processing device, and a controller for controlling a power source so as not to supply electric power to the sheet processing device and the conveyer to transport the sheet to the first discharge tray when discharging the sheet to the first discharge tray, and controlling the power source to supply power to the sheet processing device and the conveyer to transport the sheet to the sheet processing device when discharging the sheet to a second discharge tray provided on the sheet processing device.