An image reading apparatus for approximately obtaining an image signal which might have been obtained if scanned in a second direction using an image signal obtained by scanning in a first direction. The image apparatus includes a conveyer for conveying a document, a detector for detecting the inclination of the conveyed document, and a window generator for generating a window signal. Also included is an image reader for reading an image by scanning the document in a first direction at a width broader than the width of the document and reading the scanned image only when the window signal is present to produce an issuing image signal. Also included is a first corrector for adjusting the start timing of the window signal so that the window signal may be started when the scanning passes through the beginning end of the document by reference to the inclination angle of the document. Also included is a second corrector for dividing the image signal of each sweep for the first direction after the first correction into a plurality of image signal blocks linking a plurality of the image signal blocks and approximate image signal which might have been obtained if scanned in the second direction.