An outboard motor includes an engine, an exhaust passage, an idle exhaust passage, a contraction portion and an expansion chamber, a bypass passage, and a check valve. The bypass passage includes an upstream end connected to the idle exhaust passage at a downstream side relative to the contraction portion and the expansion chamber, and a downstream end connected to the idle exhaust passage at an upstream side relative to the contraction portion and the expansion chamber. The check valve is provided in the bypass passage. The check valve is arranged such that air flows only from the upstream end side to the downstream end side.