A filtration portion 11 constituting a filter element 3 is composed of a first filtration material 9 wound around the outer periphery of an inner tube 8 and a second filtration material 10 wound tightly around the outer peripheral surface of the first filtration material 9, and gas comprising oil mist is passed inside the filtration portion 11 from the inner peripheral surface to the outer peripheral surface thereof. As a result, a filter with good oil mist separation efficiency can be provided in which oil mist can be trapped and caused to condensate into oil drops with the first filtration material 9 and the oil drops can be grown with the second filtration material 10 and separated from the gas.