1. An image forming apparatus comprising: an image reader that includes a document transporting device that transports a document loaded in a loading position to a reading position, a loaded-document detector that detects whether the document has been loaded in the loading position, a document table on which the document to be read is placed, a document holder that can be closed to cover an upper surface of the document table and can be opened to make a space above the document table, has a white back face facing the document table, and holds the document placed on the document table, and a document-holder position detector that detects whether the document holder was opened within a predetermined period of time, the image reader reading an image of at least one of the document loaded in the document transporting device and the document placed on the document table; an image former that forms an image based on the image read by the image reader; an acceptor that accepts a request for the image former to perform image formation based on detecting a depression of a start key; a paper transporter that transports a paper sheet on which the image is to be formed to the image former; a mode selector that can select at least one of a first mode in which the paper transporter starts transporting a paper sheet when the image reader starts reading the image and a second mode in which the paper transporter starts transporting a paper sheet after the image reader finishes reading the image; a first controller that, when the acceptor accepts an image formation request, controls the mode selector to select the second mode and controls the image reader to read an image on the document table if the loaded-document detector detects that the document has not been loaded in the loading position and the document-holder position detector detects that the document holder was not opened within the predetermined period of time; and a second controller that, if the loaded-document detector detects that the document has been loaded in the loading position while the first controller is in operation, controls the document transporting device to transport the document in the loading position to the reading position while controlling the mode selector to select the first mode, and controls the image former to form an image based on the image of the document transported by the document transporting device and read by the image reader, wherein the predetermined period of time is set to start from a last image formation by the image former until the depression of the start key.