F₁-ATPase, which is a part of ATP synthase, catalyzes the hydrolysis of ATP by itself. F₁-ATPase is a single-molecule motor driven by the energy liberated from ATP hydrolysis. This rotation have been confirmed by a single-molecule rotation assay. By use of magnetic beads as the probe of microscopic image, the rotation of F₁-ATPase have been controlled by an electromagnetic system. It is expected that if the ATP-binding of F₁ triggers the rotation, the affinity of ATP-binding changes with the rotation angle. This feature was studied experimentally using the electromagnetic system. [DOI: 10.1380/ejssnt.2004.241]