An image reading apparatus for reading an image of an original includes an illumination portion for illuminating the original with light, a reflection member including a reflecting surface for reflecting the light from the original; a converting portion for photoelectrically converting the light reflected by the reflection member, and a casing for accommodating the reflection member. The casing is provided with an opening which is open to an outside of the casing. A surface of the reflecting member opposite from the reflecting surface and a portion defining the opening are bonded to each other with an adhesive.