PURPOSE: To accumulate a large quantity of heat by a small electric capacity for a long time by providing a heating part formed of a heat conductor of a predetermined shape having a hollow part in which heat stored fluidlike heat medium is input, stored and output.

CONSTITUTION: Heat is accumulated in liquidlike heat medium 4 by heat generated from an electric heat generator 2 in a hollow heat accumulator 1. The medium 4 is formed of inorganic salt or low melting point alloy, the salt is selected, for example, from one or more of NaNO2, NaNO3, KNO3, KNO2, NaCl, BaCl, KCl and the metal is formed of one or more of Sn, Pb. The medium 4 in the accumulator 1 is circulated through a pipe 3 by a pump 9. Further, the medium 4 is circulated through a heater 10 formed of a flat plate such as an iron plate having a hollow part. Thus, a large quantity of heat is accumulated by a small electric capacity for a long time and it can be reduced in size.