To provide a second class absorption heat pump system capable of securing a stable operation state all year round.

This second class absorption heat pump system includes an atmosphere-side heat exchanger 6a capable of exchanging heat with atmospheric air and a ground-side heat exchanger 7a capable of exchanging heat with the ground 7 by circulating a cooling medium in a condenser 4, and further includes a first cooling medium circulation controlling means 8a for allowing the cooling medium c to radiate heat through the atmosphere-side heat exchanger 6a when an atmospheric temperature is lower than a required cooling medium temperature as a temperature of the cooling medium c determined according to a temperature required for a heated medium, and allowing the cooling medium c to radiate heat through the ground-side heat exchanger 7a when the atmospheric temperature is higher than the required cooling medium temperature.