Accumulateur de chaleur et son procédé d'exploitation

Provided is a heat-storage unit capable of efficiently storing heat in a heat-storage material and sufficiently taking out the stored heat.The heat-storage unit (1) capable of exchanging heat by direct contact between sodium acetate (3) and oil (2), storing heat in the sodium acetate, and radiating heat from the sodium acetate by supplying the oil, which has a smaller specific gravity than the sodium acetate and is separated from the sodium acetate, into a heat-storage tank (10) housing the sodium acetate, which stores heat depending on a state change between solid and liquid, in an internal space, in which the unit includes: a first flow pipe (43) of a supply pipe (4), at least a part of which is provided in a lower portion of the internal space and in which the oil flows; a plurality of discharge holes (4a) which are provided for the first flow pipe and discharge the oil flowing through the first flow pipe into the sodium acetate; a second flow pipe (44) of the supply pipe (4), which is connected to the first flow pipe and discharges the oil flowing through the first flow pipe to the outside of the sodium acetate; and a valve (4b) that shuts off the second flow pipe corresponding to the state change of the sodium acetate.