Abstract: An absorption refrigerator of natural circulation type employing water as a refrigerant and lithium salt as an absorbing medium, in which a U-tube is disposed in a conduit portion between a condenser and an evaporator and is connected at one end thereof to a separator in addition to the condenser and at the other end thereof to a refrigerant reservoir. A cooling conduit extends into this refrigerant reservoir to maintain substantially constant the internal pressure of the reservoir so that the amount of the refrigerant stored in the reservoir can be controlled depending on the pressure difference between the separator side of the U-tube and the reservoir side of the U-tube. Therefore, the concentration of the lithium salt solution circulating through the refrigeration system can be controlled depending on the temperature of a heating medium supplied to a generator.