To quickly raise the temperature of a hot storage room by providing side by side an evaporator heated by cooling water circulating through an engine and a radiator and a ceramic fan heater heated by the other energy source in a cabin.

For using this on-vehicle hot storage unit, at first an on-vehicle engine is rotated, and cooling water cooling the engine so as to be at about 85C is passed through an evaporator 3. Hereby air surrounding the evaporator 3 is heated, and the temperature in a hot storage room 2 is raised by convectionally circulating this hot air in the hot storage room 2. Because the engine temperature is gradually raised, but the temperature in the hot storage room 2 is not quickly raised, simultaneously with rotation of the engine a ceramic fan heater 4 is electrified so as to heat it. Hereby, air is quickly heated, convectionally circulated in the hot storage room 2 similarly to the heated air by the evaporator 3, and hence temperature rise in the hot storage room 2 is promoted.