The application of an innovative heat-storage system with metal hydride to building, air-conditioning is investigated. Metal hydrides characteristically generate heat through the absorption process and absorb heat through the desorption process allowing the, development of a new air-conditioning system without chlorofluorocarbons. The trial system is composed of two heat-storage vessels, a "shell-and-tube-type" heat exchanger built with heat transfer fins and filled with metal hydride, and a compressor equipped for hydrogen transfer. The purpose of heat storage is to decrease the difference between electric power demand in the daytime and at night. This system transfers hydrogen using electric power at night and reverses the reaction during the day using only the pressure difference between two heat-storage vessels. The experimental results indicate that heat-storage is attained within a limited time, and the heat-storage quantity is 13.5 MJ, which is sufficient for the heat capacity to cool the 10 m(2) room for 3 hr. The stored heat per unit metal hydride volume is 289 MJ/m(3) which is sufficiently higher than the conventional, system using water or ice. In addition, the coefficient of performance of the system is 2.44.