A joint actuator includes a motor, a first gear part configured to change a direction of a rotational driving force applied by the motor and increase the applied rotational driving force, a spring member, a degree of a torsional deflection of Which is determined by a rotational. driving force supplied by the first gear part, and a second gear part configured to receive a rotational driving force according to the degree of the torsional deflection from the spring member. The first gear part includes a worm gear and a worm wheel gear configured to selectively engage with the worm gear. A joint structure includes the joint actuator mounted on a housing thereof and a joint unit coupled to the housing to be rotatably driven by the joint actuator.
