An outboard motor includes an engine cover including an upper cover and a lower cover which form an engine room and which can be separated from each other vertically, the lower cover has a bottom wall and a circumferential wall which extends upward from an outer circumference of the bottom wall, an external air inlet through which to introduce air into the engine room is provided adjacent to the outer circumference of the bottom wall, and an inside wall extends upward from the bottom wall alongside the circumferential wall so as to be opposed to the circumferential wall with the external air inlet interposed between the inside wall and the circumferential wall.