An image forming apparatus includes a main assembly to which a cartridge including a developing device for developing the latent image on an image bearing member is detachably mountable, and a transfer unit, detachably mountable to the main assembly separately from the cartridge, for transferring a developer image formed on the image bearing member. The transfer unit includes a developing device contact-and-separation mechanism for moving the developing device between a contact position, where the developer carrying member contacts the image bearing member, and a spaced position where the developer carrying member is spaced from the image bearing member. The developing device contact-and-separation mechanism includes an engaging member engageable with the cartridge and movable, with respect to the transfer unit, between a first position where the developing device is placed in the contact position and a second position where the developing device is in the spaced position.