An image reading apparatus includes a casing accommodating therein a heating mechanism for heating the interior of the casing. The heating mechanism has a heating body mounted on a guide plate along which a stimulable phosphor sheet is fed. When supplied with electric current, the heating body is heated to heat the guide plate to a predetermined temperature. An air blower is disposed in confronting relation to the heating body and is energized to circulate heated air inside the casing. A temperature detector detects the atmospheric temperature inside the casing, and when the detected atmospheric temperature becomes higher than a reference temperature preset in a controller, the controller stops supplying electric current to the heating body.