To provide an automatic document reading device for discharging documents for users to easily collect the documents to one discharge tray, when documents with different sizes are mixed and put thereon.

This device comprises document feeding and delivering means 10-17 for feeding and delivering the documents to read images at an image reading part 40, document discharging means 20-23 for discharging the read documents along a delivery path, a discharging tray 30 accommodating the discharged documents, and a document length judging means 2 for judging the length in the feeding direction of the documents on an upstream side of the discharging means. The document discharging means has a switch means 22 for selecting a plurality of branch delivery paths connected with the same discharge tray on each terminal end and a branch delivery path for feeding the documents according to the length of the document judged by the document length judging means on the upstream side of the branch delivery paths.