Provided are: an illumination device having a configuration in which a temperature rise of a radiation member is suppressed in a limited volume to thereby maintain a temperature of an LED at a predetermined value or less and an image reading device provided with the illumination device. In order to release heat generated by the LED from a substrate on which the LED is mounted, a first heat radiation plate (43) and a second heat radiation plate (47) are provided on both sides of the LED-mounted substrate; the second heat radiation plate (47), the LED-mounted substrate, and the first heat radiation plate (43) are installed in this order on a second frame (40) that supports the LED-mounted substrate, first and second heat radiation plates (43) and (47); a fan is disposed on the first heat radiation plate (43) side; when viewing the second frame (40) in a direction perpendicular to a longitudinal direction thereof, a cross-sectional profile of the second heat radiation plate (47) has an area protruding with respect to a cross-sectional profile of the first heat radiation plate (43); and the configuration is such that wind from the fan is aggressively blown against the first and second heat radiation plates (43) and (47).