An image forming apparatus comprising: a drum cartridge including a photosensitive drum and capable of being inserted into said image forming apparatus with respect to an inserting direction along a rotational axis direction of said photosensitive drum; a frame, including a front side plate provided with an opening through which said drum cartridge is inserted and extracted from and a rear side plate positioned at a downstream side of said front side plate with respect to the inserting direction, which said drum cartridge is mounted in and dismounted from through the opening of said front side plate; an optical print head including a light emitting element configured to emit light to which said photosensitive drum is exposed and including a lens array configured to focus the light onto said photosensitive drum, wherein said optical print head is movable between an exposure position where said photosensitive drum is exposed to the light by causing said light emitting element to emit the light in a state in which said optical print head is positioned relative to said drum cartridge, and a retracted position in which said optical print head is more spaced from said photosensitive drum than in the exposure position; wherein a fixed member is fixed to said front side plate as a separate member from both said optical print head and said drum cartridge, positioned at an upstream side of said optical print head with respect to the inserting direction, and provided with an opening portion for guiding a cleaning member, inserted from outside of said image forming apparatus to clean a light emergent surface of said lens array, to said light emergent surface, a portion-to-be-contacted is formed on said opening portion, and configured to be contacted by a contact portion of said cleaning member to prevent further insertion of said cleaning member toward the inserting direction after said cleaning member cleans said light emergent surface by inserting into the opening portion from outside of said image forming apparatus, the contact portion being a projection projecting upward from the cleaning member and standing on the cleaning member in a direction crossing the longitudinal direction as defined by the inserting direction. a drum cartridge including a photosensitive drum and capable of being inserted into said image forming apparatus with respect to an inserting direction along a rotational axis direction of said photosensitive drum; a frame, including a front side plate provided with an opening through which said drum cartridge is inserted and extracted from and a rear side plate positioned at a downstream side of said front side plate with respect to the inserting direction, which said drum cartridge is mounted in and dismounted from through the opening of said front side plate; an optical print head including a light emitting element configured to emit light to which said photosensitive drum is exposed and including a lens array configured to focus the light onto said photosensitive drum, wherein said optical print head is movable between an exposure position where said photosensitive drum is exposed to the light by causing said light emitting element to emit the light in a state in which said optical print head is positioned relative to said drum cartridge, and a retracted position in which said optical print head is more spaced from said photosensitive drum than in the exposure position; wherein a fixed member is fixed to said front side plate as a separate member from both said optical print head and said drum cartridge, positioned at an upstream side of said optical print head with respect to the inserting direction, and provided with an opening portion for guiding a cleaning member, inserted from outside of said image forming apparatus to clean a light emergent surface of said lens array, to said light emergent surface, a portion-to-be-contacted is formed on said opening portion, and configured to be contacted by a contact portion of said cleaning member to prevent further insertion of said cleaning member toward the inserting direction after said cleaning member cleans said light emergent surface by inserting into the opening portion from outside of said image forming apparatus, the contact portion being a projection projecting upward from the cleaning member and standing on the cleaning member in a direction crossing the longitudinal direction as defined by the inserting direction.