An apparatus body of an image forming apparatus has a first guide portion having an inlet shape corresponding to an outer shape of an engagement portion provided in a cartridge when seen in an attachment direction of the cartridge to the apparatus body and guiding the engagement portion, a second guide portion for guiding a positioning target portion which is provided on the cartridge for positioning an attachment completion position of the cartridge with respect to the apparatus body, and a movable member being at a regulation position at which a guiding path of the positioning target portion by the second guide portion is blocked is immovable from the regulation position unless being pressed by the engagement portion.