An image reading device for an image forming apparatus and capable of reading the spread pages of a book document laid on a table. Even with a book document of the kind bound by staples or wire and provided with a cover by pasting, i.e., whose spread size is smaller than two times of the cover size, the device is capable of producing attractive copied images or read images with ease by obviating black stripes at the bound portion, image displacement, image intrusion, local image omission, and needless image data.