With jumping mechanisms,soft landing motion is important to protect loads and the mechanisms.This study proposes a leg mechanism for soft landing based on biological motion.Human jumping motion with a load suggests a unique motion for soft landing.The landing model consists of two periods.Jerk is minimized in the first period and force is minimized in the second period.In comparison with other landing models,this model is specialized for soft landing motion protecting an objective part.Given all mechanisms have mass,such model is useful in practical application.For the purpose of realizing soft landing motion,this study proposes a new leg mechanism.The mechanism achieves quick variable transmission with cam and wire.Design process of the cam is explained with dynamics and computation.With the calculated cam shape,the leg mechanism can be driven by constant input voltage for simple control.Robustness against height change is also verified with landing simulation.With 50mm falling experiment,prototype leg mechanism performed soft landing without bounce motion and large sound.The acceleration profile of the body also agrees with the proposed soft landing model. With jumping mechanisms, soft landing motion is important to protect loads and the mechanisms. This study proposes a leg mechanism for soft landing based on biological motion. Human motion motion with a load suggests a unique motion for soft landing. Landing pattern consists of two periods.Jerk is minimized in the first period and force is minimized in the second period. In contrast with other landing models, this model is specialized for soft landing motion protecting an objective part. Giving all mechanisms have mass, such model is useful in practical application. For the purpose of realizing soft landing motion, this study Viaduct new leg mechanism. The mechanism achieves quick variable transmission with cam and wire. Design process of the cam is explained with dynamics and computation. Though the calculated cam shape, the leg mechanism can be driven by constant input voltage for simple control. Robustness against height change is also verified with landing simulation. ment, prototype leg mechanism performed soft landing without bounce motion and large sound. acceleration profile of the body also agrees with the proposed soft landing model.