There is provided an image reading apparatus for acquiring a read signal of an image by receiving and photoelectrically converting a light reflected from a document. The location of an alien substance on an original plate is detected based on a reflected light received by a light receiving unit adapted to receive a light reflected from a document. When an alien substance is detected, an illumination unit selectively illuminates the location in which the alien substance has been detected. Also, a message which prompts cleaning of the alien substance is displayed. A method of displaying the alien substance location are also provided. Thereby, the image reading apparatus of the present invention can assists a user in cleaning the alien substance such as a dust or dirt on the original plate.