PURPOSE: To satisfactorily execute image reading even if a document is diagonally fed by angularly displacing the reading direction of an image reading means by a driving means before an image reading operation is carried out, by which the angle formed by the reading direction of the image reading means and the direction of the document is set at a prescribed angle.

CONSTITUTION: The image reading section 15 is constituted freely angularly displaceably within an angle range of ±α around one end 25A as a fulcrum with respect to a reference direction R1, by which the reading direction R2 is made variable within the range of ±α with respect to the reference direction R1. The one corner part A at the front end 22A of the document 22 is detected in a line sensor 26 when the document 22 is transported with inclination in the longitudinal direction of the line sensor 26. Further, the other corner part B is detected when the document 22 is further transported. The image reading section 25 is displaced in angle by an angle Θ in the +α direction with respect to the reference direction R1, by which the reading direction R2 of the image reading section 25 is intersected orthogonally with the direction R4 of the document.