Patent ID: 8068260

Claim:
An image reading device comprising: a reading unit configured to scan first rectangle regions located within a maximum reading area equivalent to a maximum size of a document that can be scanned and acquire image data from the first rectangle regions; a transporting unit configured to move the reading unit to the first rectangle regions in a direction of movement opposite to a direction of movement in normal document reading; a document size judging unit configured to detect whether a document exists in each first rectangle region based on the image data acquired by the reading unit and a predetermined threshold, so that a size of the document is judged; a threshold switching unit configured to change a value of the predetermined threshold of the document size judging unit according to a result of judgment of a condition of a pressure plate which presses down a document on a document base, such that the value of the threshold is set to a first value when the pressure plate is judged as being in a closed condition, and the value of the threshold is set to a second value when the pressure plate is judged as being in an opened condition; and a pressure plate condition judging unit, wherein the reading unit is configured to scan second rectangle regions located outside the maximum reading area, the second rectangles being different from the first rectangle regions used by the document size judging unit, and to acquire image data from the second rectangle regions, and the pressure plate condition judging unit is configured to judge the opened or closed condition of the pressure plate, based on the image data of the second rectangle regions acquired by the reading unit, and wherein the reading unit is further configured to scan two rectangle regions located outside the maximum reading area and to acquire image data from the two rectangle regions, and the pressure plate condition judging unit is further configured to judge the opened or closed condition of the pressure plate based on the image data of the two rectangle regions acquired by the reading unit.