To provide an oil separator capable of improving oil separation efficiency by securing an opportunity of a collision of a gaseous refrigerant with a collision plate.

The oil separator (1) is disposed at a back stage of a compressor in a refrigerant circuit, and separates an oil component from the introduced gaseous refrigerant. The oil separator includes a casing (4) having a refrigerant inlet (2) and a refrigerant outlet (3), and a collision section (10) disposed in the casing (4) so that the gaseous refrigerant introduced into the casing (4) from the refrigerant inlet (2) can collide therewith several times. The collision section (10) has a plurality of collision faces (11) along the gaseous refrigerant advancing direction, each collision face (11) has a plurality of openings (12) through which the gaseous refrigerant passes, and the opening (12) formed at the other collision face (11) immediately below the downstream side of one collision face (11) is deviated from the opening (12) formed at one collision face (11) in the in-plane direction of the collision face (11).