An oil separator includes: an oil separator container; and a filter element that is disposed in the oil separator container, defines an outer cavity between the oil separator container and itself, includes an inner cavity into which refrigerant gas is introduced, and separates oil from the refrigerant gas flowing to the outer cavity from the inner cavity. The filter element includes a tubular inner filter member that surrounds the inner cavity, and an outer filter layer that includes a refrigerant gas outlet surface exposed to the outer cavity and is disposed outside the inner filter member. A wire-like or band-like filter retaining member that is in contact with the outer filter layer from the outside may be provided. The refrigerant gas outlet surface may occupy at least 80% of the surface area of the outer filter layer.