Some conventional image-forming devices employing an electrophotographic system have been equipped with coupling mechanisms rather than gear mechanisms for driving the photosensitive drums and the endless belt disposed in confrontation with the photosensitive drums. In this type of image-forming device, the driving force is provided for the couplings of the photosensitive drums and the coupling of the endless belt simultaneously. However, the time that elapses before the couplings of the photosensitive drums are engaged is often different from the time that elapses before the couplings of the endless belt are engaged, even if the driving force is provided for the couplings of the photosensitive drums and the coupling of the endless belt simultaneously. As the result, the time the photosensitive drums starts to rotate is different from the time the endless belt starts to rotate, which can lead to fluctuations in load applied to the photosensitive drums. The fluctuation of the load can cause problems in image formation and the like. Thus, various image-forming devices have been proposed to resolve such image-forming problems and the like resulting from this time differential.
With the electrophotographic image-forming device disclosed in Japanese unexamined patent application publication No. 2004-117644, for example, the start timing for driving an intermediate transfer belt is set earlier than the start timing for driving the photosensitive drums to avoid the occurrence of image forming problems caused by fluctuations in load applied to the photosensitive drums.