An absorption water heater/chiller using lithium bromide as an absorbent and water as a refrigerant, and a high temperature regenerator therefor. The high temperature regenerator is provided with a combustion chamber defined by an inner tube (2) on the side of a blowout port of a burner (4B), from which a combustion gas is blown out. A solution is received in a liquid chamber, which extends on upper and lower sides of the combustion chamber and is defined by an outer tube (1). A refrigerant steam outflow passage (8) is formed in an upper portion of the outer tube, and gas discharge passages (13, 14) are formed at an end portion of the combustion chamber opposed to the burner. A plurality of solution tubes (3) providing communication between the liquid chamber portions on the upper and lower sides of the combustion chamber extend through the combustion chamber. The plurality of solution tubes are roughly divided into a group (3A) provided in flame of the burner, and a group (3B) provided away from the flame of the burner. The two groups are spaced from each other by 10-100 mm. Thus reduction of Nox is achieved and generation of CO is suppressed.