A variable-stiffness actuator capable of providing different stiffnesses for a flexible member includes a shape-memory member that can transit in phase between a first phase and a second phase and an inducing member that causes phase transition between the first phase and the second phase into the shape-memory member. The shape-memory member is arranged in the flexible member with at least one free end. The shape-memory member takes a flexible state in which it is easily deformable by an external force when it is in the first stare, so as to provide lower stiffness for the flexible member. The shape-memory member takes a rigid state in which it tends to take a memorized shape memorized beforehand against an external force when it is in the second stare, so as to provide higher stiffness for the flexible member.
