Problem: it is difficult for the tooth to fly even if the other is fitted into the concave portion of the sprocket.Solution: the sprocket 39 is provided with a recess U which is located between the teeth h adjacent to the circumferential direction of the sprocket 39 and is capable of engaging the pin portion of the endless chain, and the side part 50 on the other side in the circumferential direction of the tooth h located on one side in the circumferential direction of the adjacent tooth h in the concave u A bottom portion 51 of a flat shape along the circumferential direction is provided over the side portion 52 on one side in the circumferential direction of the tooth h located on the other side in the circumferential direction, the side part 50 on the other side and the side part 52 on one side, and is provided.The length 51A of the bottom portion 51 is set to be longer than the length H1 of the root of the tooth H.Diagram【課題】スプロケットの凹部に他物が嵌まり込んでも歯飛びが生じ難いようにする。【解決手段】スプロケット39に、スプロケット39の周方向に隣接する歯Hどうしの間に位置して無端チェーンのピン部が係入可能な凹部Uが備えられ、凹部Uに、隣合う歯Hのうち、周方向において一方側に位置する歯Hの周方向での他方側の側部50と、周方向において他方側に位置する歯Hの周方向での一方側の側部52と、他方側の側部50と一方側の側部52とに亘って設けられ、周方向に沿う平坦形状の底部51と、が備えられ、底部51の周方向における長さ51aは、歯Hの根元の周方向の長さh1よりも長く設定されている。【選択図】図7
