To enhance the load resistance of an actuator, and to secure safety to an external environment.

A joint actuator 11 has a first hollow motor 13 and a second hollow motor 14 which are arranged in a housing 12. The actuator includes: a harmonic reduction gear 16 which is connected to the output side of the first hollow motor 13, and decelerates a drive force from the first hollow motor 13; a circular spline 22 which outputs the drive force decelerated by the harmonic reduction gear 16; and a twist spring 15 connected between a flexspline 23 of the harmonic reduction gear 16 and the housing 12. The second hollow motor 14 is connected to the flexspline 23 of the harmonic reduction gear 16 at its output side in parallel with the twist spring 15, and drives the flexspline 23 of the harmonic reduction gear 16.