Provided are a webbing-threading member and a seatbelt device that can prevent deviation of webbing (a so-called jamming phenomenon) by preventing rotation of the webbing-threading member. A webbing-threading member 1 of the present invention includes a body 2 rotatably mounted on the side of a vehicle, a threading hole 3 formed in the body 2 for guiding the webbing W, and a guide piece 4 placed on a surface of the threading hole 3 and forming a sliding surface 41 over which the webbing W slides. The guide piece 4 has, on the sliding surface 41, engaging grooves 42 that cause a pressing force to act in such a direction as to rotate the body 2 toward a vehicle front side at the time of withdrawing the webbing W, and that cause a pressing force to act in such a direction as to rotate the body 2 toward a vehicle rear side at the time of retracting the webbing W.