A developing blade member for regulating a thickness of a layer of a developer on a peripheral surface of a rotatable developing roller enclosing a magnet roller, wherein a scraper for scraping the developer toward longitudinally inside of the developing roller is provided at a longitudinal end of the developing roller. Monovalent compounds also comprise a macrocyclic ring, a nucleophilic moiety, and a spacer group. The objective lens reduces a first aberration introduced by the mirror, and each camera further reduces any residual first aberration. The flicker detecting section detects the flicker from the index, and controls the switching section in response to the detection result of the flicker, so that the switching section selects either the setting signals from the first imaging parameter setting section or the setting signals from the second imaging parameter setting section.