Document transport device, image reading device, and image forming apparatus

A document transport device comprising:

• a document placement table on which documents of different sizes are capable of being stacked;
• a feeding unit that is capable of moving up and down, the feeding unit being configured to send out the documents, which are stacked on the document placement table, by moving down onto the documents and to move upward after the feeding unit has sent out the documents;
• an isolation unit that transports one of the documents sent out by the feeding unit, the document being at the top of the documents, by separating the document from the other documents;
• and
• a receiving unit that receives selection of a mixed-size document mode for sending out the documents of the different sizes, which are stacked on the document placement table,
• wherein, when the receiving unit receives selection of the mixed-size document mode, the isolation unit transports one of the documents while the feeding unit is maintained in a lowered state after the feeding unit has sent out the document.