To achieve accurate determination in real time of vertical components of reactions against floors working on both individual leg bodies when the moving of a two-foot walk moving body such as a human body is supported with both the leg bodies in contact with the ground.

It is judged sequentially whether the moving of leg bodies is supported with one leg or both legs while the overall reaction is estimated based on the equation of motion for the center of gravity of the two-foot walk moving body. When the moving of the leg bodies is supported with one leg, the estimated value of the total reaction is defined as the estimated value of a reaction against the floor as for the leg bodies contacting the ground. The position (MP height) from the floor surface of the metatarsophalangeal joints at a foot flat part is measured and when the supporting is made with both legs in shift, the vertical component of the reaction against the floor as for the leg body on the rear side is estimated from the MP height of the leg body on the front side based on a specified correlation established between the MP height of the leg body on the front side and the vertical component of the reaction against the floor as for the leg body on the rear side. The vertical component of the reaction against the floor as for the leg body on the front side is estimated by subtracting the vertical component of the reaction against the floor as for the leg body on the rear side from the vertical component of the total floor reaction.