NOVELTY - The regenerator (1) has water retention airtight container that is provided with the hollow water retention housing including water retention space (22) for storing. A communication blocking unit (41,42) blocks the circulation of the water from the water retention space to the calcium compound accommodation space (12). A control unit (31) switches the blocking of the water in the calcium compound accommodation space, by controlling the communication blocking unit. The water circulation space (F1) is connected to the upper unit of the water retention space.    USE - Regenerator for high-temperature fuel cell system used in boiler system (all claimed).    ADVANTAGE - The regenerator can efficiently provide the heat to the fuel cell system and can easily discharge the stored heat, since communication blocking unit blocks circulation of water from water retention space to calcium compound accommodation space.    DETAILED DESCRIPTION - The control unit controls the communication blocking unit, so that water circulates from the water retention space to calcium compound accommodation space, when the exothermic reaction of calcium oxide and water generates a calcium hydroxide in the calcium compound accommodation space. The communication blocking unit is provided with valve positioned in water circulation space. A calcium compound accommodation airtight container (20) and the fuel cell are positioned in the heat insulation space. A water retention airtight container (L2) is positioned to the exterior of heat insulation container. INDEPENDENT CLAIMS are included for the following:    (1) high-temperature fuel cell system; and    (2) boiler system.    DESCRIPTION OF DRAWING(S) - The drawing shows the explanatory view of the regenerator.    Refrigerator (1)    Calcium compound accommodation space (12)    Calcium compound accommodation airtight container (20)    Water retention space (22)    Control unit (31)    Communication blocking unit (41,42)    Water circulation space (F1)    Water retention airtight container (L2)