PURPOSE: To provide the objective material which has a high heat-exchange efficiency while capable of storing a large amt. of heat as the heat of fusion in phase conversion by enabling an efficient heat transfer when a substance used as the material is solid.

CONSTITUTION: A particulate heat-storage material A is produced by converting a substance 1 which releases or absorbs a large amt. of heat of fusion (heat of solidification) in phase conversion such as paraffin or barium hydroxide, into particles or small blocks and coating the surfaces of the particles or small blocks with a soft rubber or synthetic resin.