An image forming apparatus comprising: a first image forming portion (PY, PM, PC) for forming an image on a photosensitive member with a developer by a developing roller; a second image forming portion for forming an image on a photosensitive member with a developer, different in color from the developer in the first image forming portion (PY, PM, PC), by a developing roller; a first gear train for transmitting a driving force to at least one of the developing roller and the photosensitive member which are provided in said first image forming portion (PY, PM, PC); a second gear train for transmitting a driving force to at least one of the developing roller and the photosensitive member which are provided in said second image forming portion; a first developing roller moving mechanism including a first developing roller moving member for moving the developing roller of said first image forming portion (PY, PM, PC) toward an associated photosensitive member and first driving force switching means for switching between a first transmission state in which a driving force is transmitted to said first developing roller moving member to move the developing roller of said first image forming portion (PY, PM, PC) and a first disconnected state in which the transmission of the driving force is disconnected; and a second developing roller moving mechanism including a second developing roller moving member for moving the developing roller of said second image forming portion toward an associated photosensitive member and second driving force switching means for switching between a second transmission state in which a driving force is transmitted to said second developing roller moving member to move the developing roller of said second image forming portion and a second disconnected state in which the transmission of the driving force is disconnected, characterized in that the driving force transmitted to said first developing roller moving member in the first transmission state is supplied from said first gear train and the driving force transmitted to said second developing roller moving member in the second transmission state is supplied from said second gear train, independently of the first gear train. a first image forming portion (PY, PM, PC) for forming an image on a photosensitive member with a developer by a developing roller; a second image forming portion for forming an image on a photosensitive member with a developer, different in color from the developer in the first image forming portion (PY, PM, PC), by a developing roller; a first gear train for transmitting a driving force to at least one of the developing roller and the photosensitive member which are provided in said first image forming portion (PY, PM, PC); a second gear train for transmitting a driving force to at least one of the developing roller and the photosensitive member which are provided in said second image forming portion; a first developing roller moving mechanism including a first developing roller moving member for moving the developing roller of said first image forming portion (PY, PM, PC) toward an associated photosensitive member and first driving force switching means for switching between a first transmission state in which a driving force is transmitted to said first developing roller moving member to move the developing roller of said first image forming portion (PY, PM, PC) and a first disconnected state in which the transmission of the driving force is disconnected; and a second developing roller moving mechanism including a second developing roller moving member for moving the developing roller of said second image forming portion toward an associated photosensitive member and second driving force switching means for switching between a second transmission state in which a driving force is transmitted to said second developing roller moving member to move the developing roller of said second image forming portion and a second disconnected state in which the transmission of the driving force is disconnected, characterized in that the driving force transmitted to said first developing roller moving member in the first transmission state is supplied from said first gear train and the driving force transmitted to said second developing roller moving member in the second transmission state is supplied from said second gear train, independently of the first gear train.