An upper cover attached to an optical box included in an optical scanning device includes a flow path in which a sealing member is injection-molded. The flow path includes a first bottom portion, a second bottom portion, and a step. The step is formed between the first bottom portion and the second bottom portion, and the area where the sealing member and the upper cover adhere to each other increases by an amount corresponding to the provided step so that adhesiveness between the sealing member and the upper cover is enhanced.