The invention provides a printing system and an extension unit that can transport media of any specified sizes. The printing system comprises a printing device; the extension unit arranged under the printing device and used for containing a medium; and a conveying path used for conveying the medium to a printing portion of the printing device. The printing device comprises the printing portion forprinting the medium by employing a recording material; a first accommodating portion for accommodating the medium; a second accommodating portion located under the first accommodating portion and used for accommodating related articles of the printing device; and a first paper supply mechanism for conveying the medium accommodated in the first accommodating portion to the conveying path. The extension unit comprises a housing; a third accommodating portion for accommodating the medium; a second paper supply mechanism for conveying the medium accommodated in the third accommodating portion tothe conveying path; and a feeding roller configured at a position overlapping with the second accommodating portion in the horizontal direction along the conveying path and used for conveying the medium conveyed from the second paper supply mechanism.