To provide an image reader which can adjust the deviation of a focal position affected by thermal expansions of respective members caused by the rising of internal temperature by providing a position information unit capable of detecting the deviation of the focal position simultaneously with a reading operation, and can read a document at a satisfactory focal position.

This image reader is provided with: a document placing face 31 on which a document 32 is disposed; a light source for irradiating the document 32 with light; one or more mirrors for reflecting reflection light from the document 32; a lens 35 for forming an image of the reflection light; and a photoelectric transducer 36 for converting image-formed reflection light into an electric signal. Further, the image reader is provided with: a moving means for moving at least one of the lens 35 and the photoelectric transducer 36; a position information unit 37 for obtaining information on at least two or more focal positions; and a control means for controlling the moving means.