1. An image reading device comprising: a first document table being transparent and supporting a document sheet on which an image is recorded; a second document table being transparent and disposed adjacent to the first document table, the second document table allowing the document sheet being transported to pass therethrough while the document sheet is kept separate from the second document table; a document transport member configured to transport the document sheet toward the second document table; and a reading unit supported on a side opposite to the document sheet with the first and second document tables interposed therebetween, the reading unit reading the document sheet, the reading unit including a movement unit movable in a preset first direction relative to the first and second document tables, wherein as a result of reading the document sheet on the first document table, the reading unit s configured to read the image on the document sheet while the movement unit is moving in the first direction, wherein as a result of reading the document sheet on the second document table, the reading unit reading the image on the document sheet transported by the document transport member while the movement unit is stopped at a position facing the second document table, wherein the first table has a first thickness and the second document table has a second thickness such that a length of a first optical path between the reading unit and the document sheet located on an upper surface of the first document table corresponds to a length of a second optical path between the reading unit and the document sheet as the document sheet is being transported by the document transport member, wherein the first thickness is different from the second thickness.
6. The image reading device according to claim 1 , wherein a lower surface of the first document table is flush with a lower surface of the second document table.