A gear attachment structure receives rotation of a handle assembly. The gear attachment structure includes a traverse cam shaft and a driven gear. The traverse cam shaft includes a shaft body, a gear support portion and a gear engaging portion. The gear support portion includes intersecting helical grooves on the outer peripheral surface. The gear support portion is disposed on an end of the shaft body and has a circular cross-section. The gear engaging portion includes a pair of circular-arc portions and a pair of straight portions. The circular-arc portions are opposed to each other while being either disposed along and within the outer periphery of the gear support portion or disposed radial outwards of the gear support portion. One of the straight portions is coupled to one ends of the circular-arc portions whereas the other of the straight portions is coupled to the other ends of the circular-arc portions.本發明之課題，係在可以簡單之機械加工來抑制齒輪構件與橫跨凸輪軸之間之旋轉方向的晃動。本發明之解決手段的齒輪裝設構造(20)，係利用擺動機構(6)來傳達旋轉柄組合體(1)之旋轉的構造。齒輪裝設構造，其係具備橫跨凸輪軸(21)、及齒輪構件之一例的從動齒輪(23)。橫跨凸輪軸(21)，其係具有軸心體(25)、齒輪支撐部(26)、以及齒輪卡止部(27)。齒輪支撐部，其係於外周面形成有交叉之螺旋狀溝(2521)者。齒輪支撐部，其係具有配設於軸心體之其中一端側的圓形剖面。齒輪卡止部，其係含有一對之相對部的圓弧部(27a)及一對之直線部(27b)。一對之圓弧部，其係以與和齒輪支撐部相同之徑方向位置或超過齒輪支撐部之徑方向的位置相對之方式來配置。一對之直線部，其係連結於一對之圓弧部的兩端。
