An image reading apparatus includes a reading unit, a controlling unit and a changing unit. The reading unit receives a reflected light from a sheet onto which a light is irradiated from a light source, converts the received light into an image signal, and accumulates a charge corresponding to the image signal in accordance with a reading time of the sheet. The controlling unit controls the light source to be turned off in accordance with a reading mode of the sheet so that an amount of the accumulated charge does not reach a saturated amount. The changing unit changes an amplification factor of an amplifying unit in accordance with a turn-off time of the light source to amplify the image signal to a predetermined level when the controlling unit controls the light source to be turned off. The amplifying unit amplifies the image signal at a predetermined amplification factor.