1. An operational space physical quantity calculation apparatus for computing a physical quantity in an operational space describing a relationship between forces and accelerations acting on a link structure including a plurality of linked rigid bodies, the apparatus comprising: a forward dynamics calculating unit configured to perform a forward dynamics calculation based on a kinetic model of the link structure, the forward dynamics calculating unit being configured to: calculate force information for a subset of the linked rigid bodies disposed between a terminal end of the link structure and a base point of the link structure, the force information corresponding to at least one force acting on the link structure; identify, based on the operational space, a reference point disposed alone the link structure, and determine an acceleration at the reference point, based on at least the calculated force information; and an operational space physical quantity computing unit configured to compute an inverse operational space inertia matrix and an operational space bias acceleration.