Abstract: A digital image forming apparatus which detects a center of a book document when reading and writing an image of the document, including a document, a document board on which the document is set, a reading device for reading the document by scanning the document, an A/D converter for converting an analog signal which is read by the reading device to a digital signal, a signal processor for processing the digital signal, including a first detector for detecting the existence of a dark portion in the image of the document and judging the document to be a book document if the document image has the dark portion, based on the signal corresponding to at least two lines on the document in a scanning direction, or in a direction perpendicular to the scanning direction and a second detector for detecting a center portion of the document on the basis of each center dark portion of each signal of the lines if the document is judged to be a book document, and a writing device for writing the digital signal on a photocon