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Bacterial flagellum is a supramolecular complex and consists of a basal body, a helical filament, and a hook. A basal body embedded in cell membrane functions as a rotary motor driven by electrochemical potential of specific ion, and rotates flagellar filament like as screw. The rotor consists of MS-ring (FliF) and C-ring (FliG, FliM, and FliN).To learn roles of the electrostatic interaction between stator and rotor in the mechanism of torque generation, we examined the motor response over the temperature range 5-50 degree. At low temperature (23-5 degree), rotational speeds linearly decreased with decreasing temperature. With increasing temperature, however, sudden drops of speeds were observed over ∼30, ∼40 and ∼50 degree. When the temperature returned back to 23 degreee, the speed was restored mostly in several minutes. The drop and recovery of the speed were coincided with stepwise change in the generated torque.And, we constructed fusion proteins of rotor components and Green Fluorescent Proteins, and investigated whether rotor components are exchanged in a functional motor by FRAP analysis for a single motor labeled with GFP.In the tethered cell that was produced each GFP fusion, a fluorescent spot was localized at the rotational center. Each GFP fusion was probably incorporated into flagellar motor as a rotor component. In order to investigate the exchange of rotor components, we carried out FRAP analysis using evanescent light. GFP-FliN or FliM-GFP recovery of fluorescence at the rotational center was observed as time passed. On the other hand, the recovery of fluorescence was not observed in the cell producing GFP-FliG. These results suggest that some rotor components assemble to motor even after functional motor is constructed.