The invention provides an illuminating device, an image-reading apparatus and an image-forming apparatus. The illuminating device includes a light-emitting element that is mounted on a base material and a light-guiding member that guides light from the light-emitting element to an irradiation target, and illuminates the irradiation target with the light transmitted through the light-guiding member. The light-guiding member includes an extending portion that extends from the surface of the base material on which the light-emitting element is mounted to a left side end portion of the base material so as to cover the left side end portion. An image-reading includes this illuminating device. Image-forming apparatus includes this image-reading apparatus.