An optical scanning device includes a casing (31). The casing (31) can be stacked in a plurality of stages in a state in which a lid member (32) has been removed, and includes a connection leg part (31e) extending from a predetermined position of the outside surface of a sidewall part (31b) to a lower side of a lower surface of the casing (31), and the connection leg part (31e) is provided with an engaged part (31g) for connection which is engaged with an engaging part (31d) formed at a sidewall part (31b) of another casing (31) when the casing (31) is stacked on an upper side of the other casing (31).