A polishing material is provided in which the dispersibility of the abrasive grains of the polishing material having, as a major component, rare earth oxides including cerium oxide is made better and the hardness of abrasive grain precipitates is reduced, and at the same time high efficiency of polishing can be achieved stably. A main CPU performs fixing control on the basis of sensing temperatures from these two thermistors. The second subsystem has an electro-mechanical actuator adapted to turn a second wheel of the vehicle. The printing device prints an image on the print medium transported by the transportation device. In such a construction, the resulting charge transport layer exhibits enhanced cracking suppression, improved wear resistance, excellent imaging member electrical performance, and improved copy print out quality. Further, since the amount of the biodegradable plastic is small and a shape such as a groove is provided which can increase a contact area with the degradative enzyme, decomposition can be completed in a short time.