To provide a thumb mechanism that enables activities nearer to the activities of a human thumb, and provide a humanoid hand incorporating this thumb mechanism.SOLUTION: When force to turn in a counterclockwise radial direction acts on a first bone member 4 (thumb mechanism), the first bone member 4 moves to a dotted position of Fig. 6 while turning counterclockwise. That is, the first bone member 4 (thumb mechanism) performs action obtained by synthesizing the turning around a center point P and the lateral movement to a center point P1. Alternatively, when the force to turn in a watch radial direction acts on the first bone member 4 (thumb mechanism), the first bone member 4 moves to the one-dot chain line position of Fig. 6 while turning in a clockwise direction. That is, the first bone member 4 (thumb mechanism) performs action obtained by synthesizing the turning around a center point P and the lateral movement to a center point P2.SELECTED DRAWING: Figure 6【課題】 人間の拇指の動きにより近い動きを可能とした拇指機構とこの拇指機構を組み込んだ人間型ハンドを提供する。【解決手段】 第１骨部材４（拇指機構）に反時計径方向に回動する力が作用すると、第１骨部材４は反時計方向に回動しつつ図６の点線位置まで移動する。つまり、第１骨部材４（拇指機構）は中心点Ｐ廻りの回動と中心点Ｐ１への横移動とが合成された動作を行う。一方、第１骨部材４（拇指機構）に時計径方向に回動する力が作用すると、第１骨部材４は時計方向に回動しつつ図６の一点鎖線位置まで移動する。つまり、第１骨部材４（拇指機構）は中心点Ｐ廻りの回動と中心点Ｐ２への横移動とが合成された動作を行う。【選択図】 図６
