A new concept was proposed for the manufacture of porous-solid-supported chemical heat storage material (PSM) that is applicable to solid base metal compounds and can maintain high reactivity and respond to volume changes. The pore structure characteristics of the carbonaceous porous-solid-supported Ca(OH)(2) chemical heat storage material (Ca(OH)(2)-PSM) prepared based on this concept were evaluated, and it was found that the Ca(OH)(2)-PSM can be made into a high-density heat storage material with a maximum CaO/C weight ratio of 2.18, and the Ca(OH)(2) is supported through thin layer dispersal primarily in pores of diameter 0.15 mu m and 30 mu m in the unsupported carbonaceous porous solid. The reactivity of this material was evaluated from its exothermic characteristics in repeated heat storage and release, and its long-term stability in form was evaluated based on optical observation after repeated heat storage and release. In evaluation of exothermic characteristics, the heat production temperature was measured in a hydration reaction under saturated steam conditions at 60 degrees C in a packed-bed reactor simulating a chemical heat storage/chemical heat pump. The results showed that the maximum temperature rise was maintained after 15 repetitions, because agglomeration was inhibited due to the support of Ca(OH)(2) in pores through thin layer dispersal. Optical observation showed that both the shape of the heat storage material particles and the Ca(OH)(2) support state were maintained in their original condition after repeated hydration/dehydration reactions, and that secondary reactions do not occur. Thus it is evident that Ca(OH)(2)-PSM functions as a high-performance heat storage material for chemical heat storage.