Multi-page circulating duplex printing method

A multi-page circulating duplex printing method used in a duplex printer, the multi-page circulating duplex printing method comprising, in order, steps of:

• printing a front side of a first document using a printing unit, and then transporting, from a first passage, the first document partially out and then back to a reverse passage;
• printing a front side of a second document using the printing unit, and then transporting, from a second passage, the second document partially out and then back to the reverse passage;
• printing a front side of a third document using the printing unit, and then transporting, from the first passage, the third document partially out and then back to the reverse passage;
• printing a reverse side of the first document using the printing unit, and then transporting, from the second passage, the first document to a discharge tray;
• printing a reverse side of the second document using the printing unit, and then transporting, from the second passage, the second document to the discharge tray;
• and
• printing a reverse side of the third document using the printing unit, and then transporting, from the second passage, the third document to the discharge tray, wherein another document or other documents, other than the first document, the second document and the third document, are printed only after the third document has been transported from the second passage to the discharge tray.