1. An operational space physical quantity calculation apparatus for computing a physical quantity in an operational space describing a relationship between a force and acceleration acting on a link structure including a plurality of linked rigid bodies, comprising: forward dynamics calculating means for performing a forward dynamics calculation on the basis of force information about a force acting on the link structure in order to obtain accelerations occurring at certain points of the link structure; and operational space physical quantity computing means for computing an inverse operational space inertia matrix and an operational space bias acceleration by causing the forward dynamics calculating means to perform the forward dynamics calculation using a kinetic model of the link structure.