Abstract: An apparatus and a method for heating and cooling with a refrigerant wherein the refrigerant is compressed by a compressor, and circulated to and from the compressor through a condenser, an expansion valve and an evaporator, in this order. A first fluid is heated with the heat generated in the condenser, and a second fluid is cooled with the cooling effect or cold generated in the evaporator. When heat is low and a temperature of the first fluid is decreased, the flow passages of the refrigerant are changed from entering into the evaporator to entering into a second heat-exchanger wherein the refrigerant is heated, and the heated refrigerant is entered into the compressor and circulated. When the cooling effect or cold is low and a temperature of the second fluid is increased, the flow passages of the refrigerant are changed from entering into the condenser to entering into a first heat exchanger wherein the refrigerant is cooled, and the cooled refrigerant is entered into the evaporator and circulated.