An oil separator that separates refrigerating machine oil contained in a gas phase refrigerant by inertia force and centrifugal force, comprising: a cylindrical pressure container comprising an upper end plate having a curved portion; a refrigerant inlet pipe that leads the gas phase refrigerant containing the refrigerating machine oil into the cylindrical pressure container, the refrigerant inlet pipe having a delivery port, wherein the direction of the opening of the delivery port is faced toward the curved portion of the upper end plate of the cylindrical pressure container; and a refrigerant outlet pipe that discharges the gas phase refrigerant from which the refrigerating machine oil is separated, wherein an angle α between a straight line along a direction of an opening of a delivery port at a tip of the refrigerant inlet pipe introduced into the cylindrical pressure container and a plane perpendicular to a central axis of the cylindrical pressure container satisfies 45° ≤ α < 90°, wherein the refrigerant inlet pipe and the refrigerant outlet pipe are provided substantially parallel with a central axis of the cylindrical pressure container and penetrate the upper end plate substantially vertically, wherein the refrigerant inlet pipe penetrates the upper end plate at a position deviated from a center of the upper end plate, wherein the refrigerant inlet pipe has a curved portion curved in a U shape within the pressure container, so that the direction of the opening of the delivery port faces upward, characterized in that an oil outlet pipe is provided in a lower end plate of the pressure container, and the refrigerant outlet pipe penetrates the center of the upper end plate, and a tip of the refrigerant outlet pipe extends further downward than the delivery port of the refrigerant inlet pipe and the direction of the opening of the tip is a vertically downward direction. a cylindrical pressure container comprising an upper end plate having a curved portion; a refrigerant inlet pipe that leads the gas phase refrigerant containing the refrigerating machine oil into the cylindrical pressure container, the refrigerant inlet pipe having a delivery port, wherein the direction of the opening of the delivery port is faced toward the curved portion of the upper end plate of the cylindrical pressure container; and a refrigerant outlet pipe that discharges the gas phase refrigerant from which the refrigerating machine oil is separated, wherein an angle α between a straight line along a direction of an opening of a delivery port at a tip of the refrigerant inlet pipe introduced into the cylindrical pressure container and a plane perpendicular to a central axis of the cylindrical pressure container satisfies 45° ≤ α < 90°, wherein the refrigerant inlet pipe and the refrigerant outlet pipe are provided substantially parallel with a central axis of the cylindrical pressure container and penetrate the upper end plate substantially vertically, wherein the refrigerant inlet pipe penetrates the upper end plate at a position deviated from a center of the upper end plate, wherein the refrigerant inlet pipe has a curved portion curved in a U shape within the pressure container, so that the direction of the opening of the delivery port faces upward, characterized in that an oil outlet pipe is provided in a lower end plate of the pressure container, and the refrigerant outlet pipe penetrates the center of the upper end plate, and a tip of the refrigerant outlet pipe extends further downward than the delivery port of the refrigerant inlet pipe and the direction of the opening of the tip is a vertically downward direction.