A document feed portion of an image reading device is capable of feeding a document placed on a first document placement portion, to a predetermined reading position. A size detection portion detects a size of the document placed on the first document placement portion. A storage processing portion stores size information indicating the size of the document detected by the size detection portion, into a predetermined storage medium. An image reading portion performs a reading process of scanning a read surface of the document placed on a second document placement portion, to read an image. A setting portion sets the size information stored into the storage medium by the storage processing portion, as size information to be used for the reading process by the image reading portion.