In this study, a chemical heat pump using a calcium oxide/carbon dioxide reaction system was discussed. In order to establish the operational conditions of heat pump, heat storage and heat generation experiments were done under various reaction pressure and temperature conditions in a packed bed reactor. Decarbonation reactivity of CaCO3 was higher at higher temperature and lower pressure, and practical reaction rate was observed at reaction temperature about 1023 K under reaction pressure of 0.1 atm. Carbonation reactions of CaO proceeded almost at the equilibrium temperature of the reaction pressure. Carbonation at temperature of 1123 K was observed at reaction pressure of 1.0 atm. Then, an analytical model based on heat and mass transfer was proposed to explain the observed phenomena during carbonation in the packed bed. The analytical model enables us to clarify the detailed behavior in the bed during carbonation. The carbonation was controlled mainly by heat transfer in the packed bed. The influence of the gas flow on heat transfer was indispensable for the analytical model. The model represented well the phenomena in the experimental packed bed reactor.