PURPOSE: To make it possible to absorb heat energy from a heat source, such as sewage at one stage cycle, and what is, more, take out heat energy efficiently at a second stage cycle by constituting a connection structure of a two stage sorption heat pump properly.

CONSTITUTION: An entire system consists of both heat pumps on a high temperature side and a low temperature side. The quantity of heat of a condenser 2 and an absorber 4 on the high temperature side are connected to a generator 7 on the low temperature side, thereby producing high temperature hot water based on a two stage heat source on the low temperature side. The heat pump on the high temperature side comprises a second generator 1, a second condenser 2, a second vaporizer 3, the second absorber 4, a heat exchanger 5 and an absorber circulation pump 6. On the other hand, the heat pump on the low temperature side comprises the first vaporizer 7, a first condenser 8, a first vaporizer 9, a first absorber, a heat exchanger and a circulation pump 12. As a heat source of the first absorber 10, each of heat exchangers 21 and 71 for the second condenser 2 and the first generator 7 is connected with a piping so as to transfer the heat. In addition, energy for a heat source, such as sewage is supplied to a heat exchanger 19 of the first generator 9.