The disclosure provides an image forming apparatus for accommodating photosensitive assembly having first assembly shaft. The image forming apparatus includes casing, fixing mechanism and cover plate. The casing has first guide groove, and the first assembly shaft is configured to be slidably disposed in the first guide groove. The fixing mechanism is movably mounted on the casing so as to be movable between a blocking state and a releasing state. The cover plate is movably connected the casing so as to be movable between an opened position and a closed position. When the cover plate is moved to the closed position, the cover plate forces the fixing mechanism to move to the blocking state to block the first guide groove and cover a bottom surface of the first guide groove so as to retain the first assembly shaft of the photosensitive assembly between the fixing mechanism and the bottom surface.