An image forming apparatus having an image forming unit, a pair of frames, and a sheet cassette, is provided. The sheet cassette has a pair of lateral walls, a first engagement portion, and a first joint portion. Space enclosed by the first engagement portion, the first joint portion, and an outer surface of one of the lateral walls is exposed toward an installation side, from which the sheet cassette is installed in the image forming apparatus. The pair of frames has a second engagement portion and a second joint portion. Space enclosed by the second engagement portion, the second joint portion, and an inner surface of the one of the frames is exposed toward a side opposite from the installation side. When the sheet cassette is in an operable position, the first engagement portion is placed in an engagement position to be engaged with the second engagement portion.