Chain detachment and chain entry are avoided, and a process for setting the length of a meshing chain is avoided, while the chain feed length can also be freely changed. A meshing chain stopper (190L) comprises a meshing chain stopper attachment part (191) and a contact-stop protrusion (192). The contact-stop protrusion (192) is contact-stopped at a contact-stop point (173A) provided on the periphery of a chain locus (L) when a pair of meshing chains (150, 150) are being driven.