When the expansion / contraction member (260) expands, the first fitting piece (ET1) moves along the first guide groove (GC1) in the direction away from the cylindrical member (205), and the first moving member (210). Moves in a direction away from the cylindrical member (205). Further, when the expansion / contraction member (260) expands, the second fitting insertion piece (ET2) moves along the second guide groove (GC2) in the direction away from the cylindrical member (205), and the second moving member ( 220) moves away from the tubular member (205). When the expansion / contraction member (260) expands in this way, the length along the Z direction of the main body (151) of the actuator device increases, and the first exoskeleton member and the second attached to the first moving member (210) The angle formed by the second exoskeleton member attached to the moving member (220) is widened. As a result, the knee joint is in an extended state. For this reason, an actuator device with a large expansion / contraction ratio can be used to assist joint motion appropriately. 膨縮部材（２６０）が膨張すると、第１嵌挿片（ＥＴ１）が、第１ガイド溝（ＧＣ１）に沿って筒状部材（２０５）から遠ざかる方向に移動し、第１移動部材（２１０）が筒状部材（２０５）から遠ざかる方向に移動する。また、膨縮部材（２６０）が膨張すると、第２嵌挿片（ＥＴ２）が、第２ガイド溝（ＧＣ２）に沿って筒状部材（２０５）から遠ざかる方向に移動し、第２移動部材（２２０）が筒状部材（２０５）から遠ざかる方向に移動する。こうして膨縮部材（２６０）が膨張すると、アクチュエータ装置の本体部（１５１）のＺ方向に沿った長さが長くなり、第１移動部材（２１０）に取り付けられた第１外骨格部材と第２移動部材（２２０）に取り付けられた第２外骨格部材とのなす角が広くなる。この結果、膝関節は伸展状態になる。このため、伸縮比の大きいアクチュエータ装置を使用し、関節運動を適切にアシストすることができる。
