We have developed a novel method to evaluate the potential profile of a molecular motor at each chemical state from only the probes trajectory and applied it to a rotary molecular motor F$_1$-ATPase. By using this method, we could also obtain the inf
ormation regarding the mechanochemical coupling and energetics. We demonstrate that the position-dependent transition of the chemical states is the key feature for the highly efficient free-energy transduction by F$_1$-ATPase.
