Abstract: A hydrogen gas extractor adapted for use with a refrigerating machine in which a high vacuum is maintained and hydrogen gas is evolved largely by corrosive reactions of a solution, comprising a case, hydrogen gas exhaust means fabricated of palladium or its alloy and gas tightly secured through the walls of said case, a connecting pipe communicated at one end with said machine and open at the other end in said case, a mass of metal contained in said case, said metal being capable of occluding hydrogen gas at ordinary temperature and releasing the same at elevated temperature, and heater means for heating both said hydrogen gas exhaust means and said metal.