To provide a document reader that reads a document conveyed to an original platen obliquely to the conveyance direction by an optical unit designed to read a fixed document without lowering read precision.

The document reader is provided with the original platen 21b made of transparent glass, an RADF 22 which has a document conveyance path slanting at an angle A1 to the top surface of the original platen 21b and sends documents one after another onto the top surface of the original platen 21b through the document conveyance path, a scanner unit which irradiates a fixed document mounted on the original plate 21a or a moving document conveyed by the RADF 22 with light to read reflected light from the document as image information, and a prism 50 which projects the reflected light incident on the original platen 21b from the moving document perpendicularly downward at an angle A3 of incidence corresponding to the tilt angle A1 of the document during the read to the document mount surface.