An oil separator includes a casing that has an inlet for air and an outlet for air, and an impingement member that is provided inside the casing. Air that contains oil is introduced through the inlet into the casing and caused to strike the impingement member so that the oil is separated from the introduced air and is recovered. The outlet opens in the horizontal direction of the casing. The oil separator further includes an L-shaped elbow member that is attached to the outlet. The elbow member protrudes in the horizontal direction from the outlet and is bent upward.