A hardness variable actuator (10) mounted on a flexible member and capable of providing different hardness to the flexible member includes a shape memory member (20) capable of changing phase between a first phase and a second phase. The shape memory member (20) includes an induction member (30) that causes a phase transition between the first phase and the second phase. When in the first phase, the shape memory member (20) assumes a soft state that can be easily deformed according to external forces, thus providing a relatively low hardness for the flexible member. Further, when the shape memory member (20) is in the second phase, the shape memory member (20) takes a hard state showing a tendency to take a memory shape memorized in advance against an external force, and therefore is relatively Provides high hardness. The hardness variable actuator (10) further includes hardness calculation means (60, 84) for calculating the hardness of the hardness variable actuator (10).可撓性部材に装着され、可撓性部材に異なる硬度を提供し得る硬度可変アクチュエータ（１０）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）と、形状記憶部材（２０）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）を備えている。形状記憶部材（２０）は、第一の相にあるときは、外力に従って容易に変形し得る軟質状態を取り、したがって、可撓性部材に比較的低い硬度を提供する。また、形状記憶部材（２０）は、第二の相にあるときは、外力に抗してあらかじめ記憶している記憶形状を取る傾向を示す硬質状態を取り、したがって、可撓性部材に比較的高い硬度を提供する。硬度可変アクチュエータ（１０）はさらに、硬度可変アクチュエータ（１０）の硬度を算出する硬度算出手段（６０，８４）を備えている。
