To efficiently store heat in a heat storage body and to sufficiently take out the stored heat.

The heat storage unit 1 is adapted so that heat can be stored in sodium acetate 3 which stores heat by state change between solid and liquid and released from the sodium acetate 3 by supplying oil 2 which is smaller in specific gravity than the sodium acetate 3 and separable from the sodium acetate 3 to a heat storage tank 1a containing the sodium acetate 3 in the internal space, and performing heat exchange by its direct contact with the sodium acetate 3. This heat storage unit comprises a third distribution pipe 43 of a supply pipe 4 at least part of which is provided under the internal space and in which the oil 2 is distributed, a plurality of discharge ports 4a provided in the third distribution pipe 43 to discharge the oil 2 distributed in the third distribution passage 43 into the sodium acetate 3, a fourth distribution pipe 44 of the supply pipe 4 connected to the third distribution pipe 43 to discharge the oil 2 distributed in the third distribution pipe 43 out of the sodium acetate 3, and a valve 4b interrupting the fourth distribution pipe 44 according to the state change of the sodium acetate 3.