A thawing cycle, wherein after reduced-pressure process (G) is carried out to reduced-pressure balanced range (B), pressure restoration process (F) is started, and when the reduced-pressure of pressure restoration process (F) reaches a lower limit (P1) at which vacuum discharge does not occur, irradiation of microwaves is started, and after pressure restoration is carried out to a preset pressure restoration upper limit (D), reduced-pressure process (G') is carried out once again, and irradiation of microwaves continues until the reduced-pressure reaches a lower limit (P1) at which vacuum discharge does not occur, and sublimation cooling by sublimation is carried out in the reduced-pressure process to reduced-pressure balanced range (B') after the irradiation of microwaves is terminated, is carried out repeatedly.