An invert rectifier is provided in which: cooling medium vapor sent from the evaporator is contacted with a weak solution sent from the regeneration unit, and the temperature of cooling medium vapor and the vapor component of absorbent are increased by the action of invert rectification, so that the enthalpy of cooling medium vapor supplied to the vapor-liquid mixer is enhanced. In this invert rectifier, cooling medium vapor is introduced to a lower portion of the container and a residual portion of the weak solution or all weak solution is introduced to an upper portion of the vapor-liquid mixer 16, so that the introduced cooling medium vapor and weak solution are subjected to vapor-liquid contact by the action of an opposed flow. Due to the foregoing, cooling medium vapor is generated, the temperature of which is high, and the amount of the vapor component of absorbent of which is large, so that the enthalpy of cooling medium vapor is enhanced. Even when the thus obtained cooling medium vapor is mixed with a weak solution in the vapor-liquid mixer 16, the temperature is seldom lowered in the mixing process, and an amount of heat exchange in the absorption regeneration heat exchanging section is increased, and the result coefficient is enhanced.