PURPOSE: To eliminate the occurrence of an inferior sheet due to poor paper joining by joining old paper to new paper with any angle not perpendicular to the side lines of thick paper that runs in a paper joining unit.

CONSTITUTION: A paper conveying bar 9, an upper nipper 10, and a knife 11 are set diagonal to the side lines of running paper. For new thick, paper M, adhesive P, is also stuck diagonally so that the joint part is joined with any angle not perpendicular to the side lines of the thick paper. By joining the paper like this, while the paper passes between upper and lower rolls 14 and 15 to be pressed into a stepped form, the overlapping joint part passes between the upper and lower rolls one part after another instead of passing its entire width simultaneously. This alleviates the shock to the upper and lower rolls given by the paper joint.