PURPOSE: To produce a heat accumulation material having effectively suppressed supercooling phenomenon of a latent heat type heat-accumulation material, by adding a nucleation agent and a surfactant to a latent heat type heat accumu lation material and temporarily melting the heat-accumulation material thereby uniformizing the dispersion state of the nucleation agent.

CONSTITUTION: (A) A latent heat type heat accumulation material (e.g. inorganic hydrate CaCl2.6H2O) is added with (B) a nucleation agent (preferably crushed or granulated to an average particle diameter of ≤0.5mm) and (C) a surfactant (e.g. a polyethylene glycol derivative) and the heat accumulation material is temporarily melted and the nucleation agent is homogeneously dispersed in the material to obtain the objective heat accumulation material. The amount of the component C is preferably 0.01W20wt% based on the latent heat type heat accumulation material.