To provide a heat control device capable of accurately deciding that heat storage material failure occurs, in the decision whether the heat storage material failure occurs.

A heat storage material 6 having completed addition of water is heated in a reactor 5 being sealed, and then a rising mode of a pressure in the reactor 5 during the heating differs in response to a presence of failure in a crystal structure of the heat storage material 6 (heat storage material failure). In other words, when the heat storage material is abnormal, a sudden rise in the pressure in the reactor 5 associated with the heating of the heat storage material 6 is started at a temperature of the heat storage material 6 lower than that when the heat storage material is not abnormal. In heat-storage-material failure decision processing for determining the presence of the heat storage material failure, taking into account that the rising mode of the pressure in the reactor 5 during the heating differs in response to the presence of the heat storage material failure, the presence of the heat storage material failure is decided based on a pressure at the time.