The variable stiffness actuator (10； 10A) has a shape memory member (20) in which the phase can change between the first phase and the second phase. When the shape memory member is in the first phase, the shape memory member is in a low rigidity state, and when in the second phase, the shape memory member is in a high rigidity state, which is a state having higher rigidity than the low rigidity state. The variable stiffness actuator further includes an induction member (30) that causes the shape memory member to cause a phase transition between the first phase and the second phase, and a connection that elastically connects the shape memory member and the induction member. It has members (40, 40A, 40B, 40C, 40D, 40E, 40F, 40G, 40H, 40I； 60). The shape memory member, the induction member, and the connection member are all conductive, and the shape memory member, the induction member, and the connection member are electrically connected.剛性可変アクチュエータ（１０；１０Ａ）は、第一の相と第二の相の間で相が移り変わり得る形状記憶部材（２０）を有している。形状記憶部材は、第一の相にあるときは、低剛性状態を取り、第二の相にあるときは、低剛性状態よりも高い剛性を持つ状態である高剛性状態を取る。剛性可変アクチュエータはさらに、形状記憶部材に第一の相と第二の相の間の相の移り変わりを引き起こさせる誘起部材（３０）と、形状記憶部材と誘起部材を弾性的に接続している接続部材（４０，４０Ａ，４０Ｂ，４０Ｃ，４０Ｄ，４０Ｅ，４０Ｆ，４０Ｇ，４０Ｈ，４０Ｉ；６０）を有している。形状記憶部材と誘起部材と接続部材はいずれも導電性を有しており、形状記憶部材と誘起部材と接続部材は電気的に接続されている。
