PURPOSE: To enable a latent heat accumulation material in a heat accumulation device to be transported up to a radiator without using any special pump.

CONSTITUTION: This heat accumulation device is comprised of a heat accumulation tank 1 having a heat exchanger 2 in it, a storing tank 11 disposed at an upper part of the heat accumulation tank 1, a pipe 6 connecting the heat accumulation tank 1 with the storing tank 11, a heat radiation part 10 disposed in the midway part of the pipe 6 and a pump 7 for flowing medium 4 within the pipe 6. The medium 4 storing heat at the heat accumulation tank 1 is thermally radiated at a heat radiation part 10, fed to the storing tank 11, the medium 4 stored in the storing tank 11 is returned back to the heat accumulation tank 1. As the medium 4, the heat accumulation material having phase varying material melted at a higher temperature than that of the liquid of continuous phase is dispersed to liquid of continuous phase.