Heat storage system and installation method of latent heat storage material therefor

A heat storage system 1 comprising: an indoor space (IDS); a heat storage space (HSS) adjacent to the indoor space (IDS) and having arranged therein latent heat storage material (H) having a melting point or freezing point that is in the range of 5–30°C; and a natural ventilation device (NV) that controls the introduction and blocking of external air to the heat storage space (HSS). The thermal resistance between the heat storage space (HSS) and external air is made greater than the thermal resistance between the heat storage space (HSS) and the indoor space (IDS).