PURPOSE: To read a thick book-type original, too, by constituting so that a guide for guiding a scanning body can be moved up and down in accordance with height of an original sheet holding plate.

CONSTITUTION: A shaft mount 26 for supporting an end part of a guide rail for guiding a scanning body 4 consists of a fixed member 26a which is fixed to the body, and a moving member 26b which can be moved up and down against the body, and these members are capable of sliding up and down mutually by a guide groove 26c. Also, a spring 26e placed around a guide rod 26d is installed in a compressed state between the upper plate of the fixed member 26a and the lower plate of the moving member 26b. Accordingly, the moving member 26b is always depressed downward elastically, and also when force is put upward, it can be moved upward.