An image forming apparatus includes a photosensitive member, a charging member, an exposure unit, a developing unit including a developing member, a motor, a contact and separation unit, a controller, an acquiring portion for acquiring information on a switching time which is a time required for switching a state of the developing member from a separated state to a contact state by executing a contact operation by the contact and separation unit, and a setting portion for setting, on the basis of the information on the switching time acquired by the acquiring portion, a start timing which is a timing when the contact operation by the contact and separation unit is started in a preparation operation and which is a timing before a region on the photosensitive member exposed to light in a light emission period reaches a developing position.