An oil separator is provided, which can accurately control an interval between an introduction hole of a gaseous body and a separation member, and can ensure a stable and high separation performance. An oil separator 30 includes a wall portion 31 having a plurality of orifices 32, and a holding portion 34 holding a separation member 33. A facing surface 33A of the separation member 33 is disposed along a front face portion 42A of a positioning portion 42 having a plurality of opening portions 42D, so that an interval L between the orifices 32 and the facing surface 33A of the separation member 33 accurately has a desired distance. A gas separated from an oil smoothly flows downward along a flow path formed by the opening portions 42D so as to reduce a pressure loss.