A sheet feeding device is operable to feed a sheet medium to an image forming apparatus. A cassette chamber has an inner face. A cassette member is adapted to accommodate the sheet medium therein, and to be withdrawably inserted into the cassette chamber in a first direction. The cassette member has an outer face adapted to oppose the inner face of the cassette chamber when the cassette member is inserted into the cassette chamber. At least one recess is formed on one of the inner face of the cassette chamber and the outer face of the cassette member. At least one protrusion is formed on the other one of the inner face of the cassette chamber and the outer face of the cassette member, and adapted to be fitted with the recess when the cassette member is plenarily inserted into the cassette chamber.