The method stores heat in ice by freezing water through its direct contact with a hardly-water-soluble refrigerant; i.e., water is mixed with the refrigerant at a high pressure to produce a liquid mixture while preventing evaporation of the refrigerant, and the liquid mixture is jetted from a nozzle into a space at a lower pressure, whereby the refrigerant evaporates at the lower pressure and the water in the liquid mixture is frozen into sherbet-like ice and dispersed over a wider area than in the case of non-sherbert-like ice. A device based on the method uses a heat-insulating water tank whose top space above water level therein is kept at a pressure P2 lower than saturation pressure P0 (P2