To provide a small-sized and inexpensive rotary actuator and a walking robot with the rotary actuator, capable of reducing damage of a gear of a gear train by reducing continuous impact from an output shaft, exhibiting the effect as a clutch by sliding even if excessive large force is applied from the output shaft to the gear train side, and of reducing partial abrasion on a part of a final stage gear.

This rotary actuator 50 to be arranged on a second member 32 in order to rotate the second member 32 in relation to a first member 30 is provided with a motor 60; an output shaft 10 connected to the first member 30 side and for rotating the second member 32 in relation to the first member 30 by the rotation of the motor 60; a gear train 80 arranged between a rotary shaft of the motor 60 and the output shaft 70, for decelerating the rotation of the motor 60, and having a final stage gear 88 positioned on the output shaft 70 side; and a cushioning mechanism part 100 arranged between the final stage gear 88 of the gear train 80 and the output shaft 70 and for cushioning impact from the output shaft 70.