A control unit performs a reading operation in a first mode in which a document on a document stand is read by moving a carriage which includes a reading portion, and in a second mode in which a document which is transported by a document transport unit is read using the carriage which is located at a reading position. The device includes a first white reference plate which is arranged in a first white reference reading position which is a standby position in the first mode, and a second white reference plate which is arranged on a side opposite to the first white reference plate by interposing a reading position in the second mode therebetween in the sub-scanning direction.