A reading unit (3) placed on the inner side of a U-shaped feed path (12) that feeds a document is formed such that the height-axis dimension of said reading unit decreases in a direction extending toward a side having a paper delivery tray (11). Contact glass (20), a light source and a first mirror (24) are placed in the reading unit (3) at an end portion of the side having the paper delivery tray (11). Multiple reflecting mirrors (25, 26 and 27), a lens (28) and a photoelectric converter element (29) are placed further from the paper delivery tray than the first mirror (24) in the reading unit. This structure enables the reading unit provided in a document feeder to be more compact while ensuring the required light path length, and enables the entire document feeder to be more compact.