A variable stiffness device includes a first elongated member, and a second elongated member movable along the first member. The first member includes first high bending stiffness sections, first low bending stiffness sections, and a reinforcement member reinforcing a strength of the first member. The reinforcement member includes a contact coil formed of a first wire spirally wound around a longitudinal axis of the reinforcement member, and a stranded tube formed of second wires that are twisted around each other. The second member includes a second high bending stiffness section, and a second low bending stiffness section. The second member is configured to move inside the reinforcement member, thereby changing a stiffness of the variable stiffness device.