PURPOSE: To prevent a damage of cooling pipe or a regenerative tank caused by a blocking of adhesion to the cooling pipe by a method wherein a circuit changing-over means is provided for changing-over a flowing direction of a regenerative refrigerant during regenerative operation and heat accumulation recovering cooling operation to an inverse direction.

CONSTITUTION: During a regenerative operation, on-off control means 16 of a circuit changing- over means 15 is operated to cause the refrigerant passed through a compressor 2 and an outdoor heat exchanger 3 to be reduced in its pressure through a second electronic expansion valve 12, thereafter the refrigerant is supplied from an indoor connection part 10c into a cooling pipe 10a, a heat exchanging operation is carried out with it between water W within a heat storing tank 9. Ice I is adhered and produced at a surface of the cooling pipe 10a to store cold heat. At this time, an amount of ice I adhered to the cooling pipe 10a is increased toward an outdoor connecting end 10b. After this regenerative operation, if the heat recovering and cooling operation is carried out, the supplied refrigerant from the outdoor connecting end 10b to the regenerative tank 10a by the action of the on-off control means 16 is heat exchanged with the ice I stored within the thermal storing tank 9 and cooled in it. Accordingly, since refrigerant of hot temperature is flowed into the cooling pipe 10a adjacent to the outdoor connecting end 10b having much volume of ice and then a melting of the ice I is promoted.