A plurality of energy efficiencies of an electric motor which are determined by characteristics of the electric motor are set according to the revolution speed and the driving force of the electric motor, and among the plurality of energy efficiencies, a plurality of energy efficiency groups having the equivalent energy efficiency are prepared. When imaging is not performed, the switching device makes the light incident on the optical finder mechanism. , a permanent magnet or the like. The radio relay apparatus determines the received identification code as a formal identification code of the radio relay apparatus. The twists are inhibited from being transported oppositely to the thread path direction and are regularly conveyed to the storage drum in almost perfect match with the rotations of the central shaft.