A device (18) for absorbing floor-landing shock provided in a foot mechanism (6) of a leg of a robot. The device comprises an inflatable/ deflatable bag-like member (19) (variable volume body) on the ground contact surface side of the foot mechanism (6). The bag-like member (19) is formed of an elastic material such as rubber. Air in the atmosphere can flow in and out of the bag-like member (19) through inflow/ outflow means (20) provided with a solenoid valve (27) etc. When the foot sole mechanism (6) is on the floor and immediately after the mechanism is changed from an on-floor state to an off-floor state, the solenoid valve (27) is closed and the bag-like member (19) is kept compressed. When the bag-like member (19) is inflated while the foot mechanism (6) is off the floor, the timing at which the solenoid valve (27) is changed from an opened state to a closed state is controlled so that the height in the compression direction of the bag-like member (19) is controlled to a height appropriate to the gait form of the robot. The shock load when the leg of the legged mobile robot lands on the floor is reduced appropriately while at the same time posture stability of the robot can be ensured easily, and, further, the robot can be structured light in weight.