A paper tube manufacturing machine of the present invention has: a transfer path for guiding transfer of a paper web having multiple cut grooves; and a web bending device for bendings the paper web and forming the paper web into a paper tube, and the web bending device includes a garniture belt, a tube forming section, and an applicator. The tube forming section, in the course of the transfer of the paper web, forms the paper web continuously into a paper tube using the garniture belt while maintaining the inner surface of the paper web in a free state, and thereby the paper tube has a lapped portion where both side edges of the paper web are lapped. Meanwhile, the applicator applies an adhesive to one of both side edges of the paper web before the lapped portion is formed, to thereby bond the both side edges with each other in the lapped portion.