To provide a heat-storage unit having excellent heat-storage capacity, free from the leakage of the heat-storage material and having excellent processability and workability.

The heat-storage unit is produced by supporting a heat-storage material (ii) on a three-dimensional crosslinked structure material (i) produced by reacting (a) cellulose and/or its derivative with (b) a compound having a functional group reactive with the hydroxy group of the component (a).