Heat source material composition, and auxiliary heat source and heat supply method using the same

A heat storage material composition, at least containing at least one organic compound selected from ethanol, ethylene glycol, propylene glycol, and acetic acid, sodium acetate, and water, wherein a content of the water is 72.4 to 100 parts by mass, relative to 100 parts by mass of the sodium acetate; an auxiliary heat source and a heat supply method, using the heat storage material composition.