Patent ID: 7656562

Claim:
An image reading apparatus comprising: a conveying unit which conveys an original; a first reading unit including a first reading section which reads one side of the original conveyed by the conveying unit; a second reading unit including a second reading section which reads the other side of the original conveyed by the conveying unit; and a moving mechanism which displaces relative positions of the first reading unit and the second reading unit in an original conveyance direction by using a driving force of a motor for driving the conveying unit, wherein, the first reading unit integrally includes the first reading section and a first reference member serving as a shading reference; the second reading unit integrally includes the second reading section and a second reference member serving as a shading reference, said moving mechanism displaces relative positions of the first reading unit and the second reading unit to a first relative position where the first reading section is opposed to the second reference member and the second reading section is opposed to the first reference member in an operation mode for determination of a shading reference, said moving mechanism displaces relative positions of the first reading unit and the second reading unit to a second relative position where the first reading section is not opposed to the second reference member and the second reading section is not opposed to the first reference member in an operation mode for reading the original, and wherein said moving mechanism contains a one-way clutch that delivers force for displacement of said relative positions, said one-way clutch being arranged on a rotary driving shaft related to conveyance of the original.