A printing apparatus and a roll paper transportation device which reduces the space needed to accommodate a roll paper buffer mechanism unit and paper detection unit, and to reduce poor electrical contact in the contact part of the paper detection unit. The roll paper transportation device has a paper detection unit for detecting the presence of roll paper. The paper detection unit itself comprises a detection lever that pivots rotationally when in contact with the roll paper, a cam formed integrally with the detection lever and having a curved surface that is concentric to the rotary axis of the detection lever, and a switch lever that contacts the curved surface of the cam.