To provide a less-expensive screw freezer having an oil tank including an oil strainer therein in which an oil cycle system is simplified and its reliability in operation is improved.

A screw freezer is constructed such that oil contained in refrigerant gas is separated by an oil separator, oil fed out to a separate type oil tank 1 is cooled with an oil cooler and an oil supplying system based on a differential pressure between a discharging pressure and a low pressure is employed in an oil circulating system for supplying oil to a rotor of a screw compressor and a sliding part of a bearing through an oil supplying pipe, wherein an oil strainer 5 is stored in the separate type oil tank 1, assuring of filtering area corresponding to an amount of supplied oil is enabled in response to a variation in length under active application of an elongated oil tank and then the oil distributing pipe is simplified.