A paper web threading apparatus for a rotary printing press comprises a paper web threading member guide provided along a paper web threading path of the printing press extending from a paper web supply section to a position just in front of a folding section; a paper web threading member pooling section provided downstream of the paper web threading path; a paper web threading member which is located over the whole length of the paper web threading path extending from the most upstream position thereof to the paper web threading member pooling section upon commencement of the paper web threading operation and which is run along the paper web threading member guide towards the paper web threading member pooling section during the paper web threading operation; a paper web retaining member provided on the paper web threading member for securing the paper web to the threaded along the path; and at least one paper web threading member driving unit for running the paper web threading member along the paper web threading member guide. Thus, this paper web threading apparatus enables a paper web to be threaded along the paper web threading path smoothly at nearly constant speed without applying uneven tension to the paper web.