A landing shock absorbing device 18 disposed in a foot mechanism 6 of a leg of a robot, wherein an inflatable bag-like member 19 (a variable capacity element) is provided at a ground-contacting face side of the foot mechanism 6. The bag-like member 19 is constructed of an elastic material such as rubber and has a restoring force. An interior portion of the bag-like member 19 is communicated with the atmosphere side through a flow passage 20. During a landing motion of the leg, the bag-like member 19 makes contact with the ground to be compressed, and the air in the interior portion thereof flows out into the atmosphere through the flow passage 20, so that its outflow resistance is generated. Accordingly, a landing shock is reduced. In a lifting state of the leg, the restoring force of the bag-like member 19 allows the bag-like member 19 to be inflated while the air flows into the interior portion thereof. An impact load during the landing of the leg of the legged mobile robot may smoothly be reduced in a light-weight configuration.