An optical scanning device includes a housing and a cover. An engaging hole is formed in the housing and an engaging piece is formed in the cover. The engaging piece has a first portion following a side wall portion of the housing and a second portion folded so as to face the first portion at an interval. When the engaging piece has been inserted into the engaging hole, the first portion is elastically deformed toward the side wall portion of the housing, and the second portion is elastically deformed toward the first portion and abuts a lower portion of an inner edge of the engaging hole, so that the engaging piece and the engaging hole are engaged with each other and the cover is pressed with respect to the housing by the restoring force of the engaging piece.