A driving force calculating device (1) includes: a setting information acquiring section (23) which acquires (a) muscle specifying information that specifies a target muscle, which is a muscle whose function is assisted or resisted by a driving section and (b) a target value of muscle force to be produced by the target muscle at the time of rotational motion under assistance or resistance of the driving section; and a target muscle force evaluating section (24) which acquires an estimated muscle force table (58) and musculoskeletal model data (53) and evaluates the feasibility of the target value of the target muscle. With this arrangement, it is possible to reduce time required to calculate a driving force of the driving section of the power assisting device.