Displacements of respective joints corresponding to respective joint elements (J9 and the like) of a rigid
link model (S1) representing a two-legged walking mobile body (1) are sequentially grasped. Also at the same time, values, in a body coordinate
system (BC), of an acceleration vector of the origin of the body coordinate
system (BC) fixed to a
waist (6) as a rigid element, a floor reaction
force vector acting on each leg (2), and a position vector of the point of application of the floor reaction
force vector are sequentially grasped. With the use of the grasped values, joint moments respectively generated in an
ankle joint (13), a
knee joint (14), and a hip joint (9) of each leg (2) are sequentially estimated based on an
inverse dynamics model using the body coordinate
system. The
estimation accuracy of the joint moments of the leg can be enhanced by reducing arithmetic
processing using tilt information of the two-legged walking mobile body relative to the gravity direction as much as possible.