The operability of a thermally driven chemical heat pump using the magnesium oxide/water reaction system was demonstrated experimentally. The heat pump system, consisting of a packed bed reactor and a water reservoir, was operated thermally with no mechanical work. The thermal output performance of the reactor bed was measured under pressures between 50 and 202 kPa. The heat pump was expected to be applicable as a heat storage system for high efficiency energy utilization In cogeneration.