A raw material gas liquefying device comprising: a feed line in which a raw material gas flows through a raw material flow path of a heat exchanger (81;82;83;84;85;86), a liquefied refrigerant storage tank which stores a liquefied refrigerant therein, and a feed system Joule-Thomson valve in this order; a refrigerant circulation line including a refrigerant liquefaction route and a cryogenic energy generation route, wherein in the refrigerant liquefaction route, a refrigerant flows through a compressor (32,33), a high-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86), a circulation system Joule-Thomson valve, the liquefied refrigerant storage tank, and a first low-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86) in this order, and returns to the compressor, while in the cryogenic energy generation route, the refrigerant flows through the compressor, an expansion unit (37;38), and a second low-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86) in this order, and returns to the compressor; a temperature sensor which detects a temperature of the refrigerant at an exit side of the high-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86) or a temperature of the raw material gas at an exit side of the raw material flow path of the heat exchanger (81;82;83;84;85;86); a liquid level sensor which detects a refrigerant storage tank liquid level which is a liquid level in the liquefied refrigerant storage tank; and a controller which determines whether or not the refrigerant storage tank liquid level is within a predetermined allowable range, manipulates an opening rate of the feed system Joule-Thomson valve to control the temperature detected by the temperature sensor so that the temperature reaches a predetermined temperature set value in a case where the refrigerant storage tank liquid level is within the predetermined allowable range, and manipulates the opening rate of the feed system Joule-Thomson valve to control the refrigerant storage tank liquid level so that the refrigerant storage tank liquid level falls into the predetermined allowable range in a case where the refrigerant storage tank liquid level is outside the predetermined allowable range. a feed line in which a raw material gas flows through a raw material flow path of a heat exchanger (81;82;83;84;85;86), a liquefied refrigerant storage tank which stores a liquefied refrigerant therein, and a feed system Joule-Thomson valve in this order; a refrigerant circulation line including a refrigerant liquefaction route and a cryogenic energy generation route, wherein in the refrigerant liquefaction route, a refrigerant flows through a compressor (32,33), a high-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86), a circulation system Joule-Thomson valve, the liquefied refrigerant storage tank, and a first low-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86) in this order, and returns to the compressor, while in the cryogenic energy generation route, the refrigerant flows through the compressor, an expansion unit (37;38), and a second low-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86) in this order, and returns to the compressor; a temperature sensor which detects a temperature of the refrigerant at an exit side of the high-temperature-side refrigerant flow path of the heat exchanger (81;82;83;84;85;86) or a temperature of the raw material gas at an exit side of the raw material flow path of the heat exchanger (81;82;83;84;85;86); a liquid level sensor which detects a refrigerant storage tank liquid level which is a liquid level in the liquefied refrigerant storage tank; and a controller which determines whether or not the refrigerant storage tank liquid level is within a predetermined allowable range, manipulates an opening rate of the feed system Joule-Thomson valve to control the temperature detected by the temperature sensor so that the temperature reaches a predetermined temperature set value in a case where the refrigerant storage tank liquid level is within the predetermined allowable range, and manipulates the opening rate of the feed system Joule-Thomson valve to control the refrigerant storage tank liquid level so that the refrigerant storage tank liquid level falls into the predetermined allowable range in a case where the refrigerant storage tank liquid level is outside the predetermined allowable range.