Provided is a document reading device capable of performing shading correction and making it difficult for foreign matters to enter inside the device. A document reading device includes a reading unit, a glass unit, and a closing member. The reading unit has a light source and reads a document. The glass unit has a glass plate that transmits light emitted from the light source and a reference member serving as a reference for shading correction of a reading optical system. The glass unit is disposed with a space provided with respect to the reading unit and slid between a first position where the light emitted from the light source transmits the glass plate and a second position where the light emitted from the light source reaches the reference member with the space being maintained. The closing member is positioned downstream of the glass plate and the reference member of the glass unit in a document conveying direction and fills at least a part of the space provided between the reading unit and the glass unit.