A heat storage system comprising: a tank configured to store a liquid so as to form temperature stratification with a high temperature upper side and a low temperature lower side; heating means for heating the liquid; a first heat utilization path (5, 32, 307a, 307b) configured to use heat stored in a first region that is a part on a upper side in the tank; a second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) configured to mainly use heat stored in a second region below the first region in the tank; a lower feed path (31, 71, 301a, 301b) configured to take out the liquid through a pipe connected to a lower portion of the tank, the lower feed path (31, 71, 301a, 301b) being configured to feed the liquid to the heating means; a middle feed path (31, 71, 301b, 308a, 308c) configured to take out the liquid through a pipe connected to a middle height portion of the tank, the middle feed path (31, 71, 30ab, 308a, 308c) being configured to feed the liquid to the heating means; feed path switching means for switching between the lower feed path (31, 71, 301a, 301b) and the middle feed path (31, 71, 301b, 308a, 308c); an upper return path (72, 301c, 301d) configured to return the liquid heated by the heating means through a pipe connected to an upper portion of the tank into the tank; and control means for performing a first region heating operation for feeding the liquid to the heating means using the middle feed path (31, 71, 301b, 308a, 308c), and returning the liquid heated by the heating means into the tank using the upper return path (72, 301c, 301d); characterized in that the control means is configured to: predict whether a heat storage amount for a demand of the first heat utilization path (5, 32, 307a, 307b) is sufficient or insufficient; predict whether a heat storage amount for a demand of the second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) is sufficient or insufficient; and perform, when it is predicted that the heat storage amount for the demand of the first heat utilization path (5, 32, 307a, 307b) is insufficient while the heat storage amount for the demand of the second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) is sufficient, the first region heating operation. a tank configured to store a liquid so as to form temperature stratification with a high temperature upper side and a low temperature lower side; heating means for heating the liquid; a first heat utilization path (5, 32, 307a, 307b) configured to use heat stored in a first region that is a part on a upper side in the tank; a second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) configured to mainly use heat stored in a second region below the first region in the tank; a lower feed path (31, 71, 301a, 301b) configured to take out the liquid through a pipe connected to a lower portion of the tank, the lower feed path (31, 71, 301a, 301b) being configured to feed the liquid to the heating means; a middle feed path (31, 71, 301b, 308a, 308c) configured to take out the liquid through a pipe connected to a middle height portion of the tank, the middle feed path (31, 71, 30ab, 308a, 308c) being configured to feed the liquid to the heating means; feed path switching means for switching between the lower feed path (31, 71, 301a, 301b) and the middle feed path (31, 71, 301b, 308a, 308c); an upper return path (72, 301c, 301d) configured to return the liquid heated by the heating means through a pipe connected to an upper portion of the tank into the tank; and control means for performing a first region heating operation for feeding the liquid to the heating means using the middle feed path (31, 71, 301b, 308a, 308c), and returning the liquid heated by the heating means into the tank using the upper return path (72, 301c, 301d); characterized in that the control means is configured to: predict whether a heat storage amount for a demand of the first heat utilization path (5, 32, 307a, 307b) is sufficient or insufficient; predict whether a heat storage amount for a demand of the second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) is sufficient or insufficient; and perform, when it is predicted that the heat storage amount for the demand of the first heat utilization path (5, 32, 307a, 307b) is insufficient while the heat storage amount for the demand of the second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) is sufficient, the first region heating operation. predict whether a heat storage amount for a demand of the first heat utilization path (5, 32, 307a, 307b) is sufficient or insufficient; predict whether a heat storage amount for a demand of the second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) is sufficient or insufficient; and perform, when it is predicted that the heat storage amount for the demand of the first heat utilization path (5, 32, 307a, 307b) is insufficient while the heat storage amount for the demand of the second heat utilization path (41, 42, 303a, 303b, 304, 305a, 305b) is sufficient, the first region heating operation.