A hot water supply system comprising: - a hot water storage tank that is adapted to store water; - a boiling unit that is a heating source that is adapted to heat the water stored in the hot water storage tank; and - a controller that is adapted to determine an amount of heat to be generated by the boiling unit, for each time slot by calculating a hot water supply load pattern that is typical for the user, in order to heat the water stored in the hot water storage tank, wherein the controller includes: - a data measurement unit that measures a water temperature and a flow rate; - a hot water supply load data storage unit that is adapted to store hot water supply load data generated on the basis of at least a water temperature of water flowing into the hot water storage tank and a water temperature and a flow rate of water flowing out from the hot water storage tank, for a plurality of days; - a hot water supply load data analysis unit that is adapted to analyze the hot water supply load data for the plurality of days stored in the hot water supply load data storage unit; - an operation plan generation unit that is adapted to predict a hot water supply load for a predetermined day ahead of the plurality of days stored in the hot water supply load data storage unit, on the basis of the analysis by the hot water supply load data analysis unit, and to generate an operation plan for the boiling unit at the predetermined day on the basis of a result of prediction; and - an operation plan correction unit that, after start of operation based on the operation plan, is adapted to predict a subsequent hot water supply load at the predetermined day on the basis of an obtained hot water supply load result at the predetermined day, and to change the subsequent operation plan at the predetermined day generated by the operation plan generation unit, on the basis of the hot water supply load predicted again and a remaining amount of stored hot water in the hot water storage tank, and characterised in that: wherein the hot water supply load data analysis unit is adapted to classify the hot water supply load data for the plurality of days stored in hot water supply load data storage unit, into a plurality of groups, the operation plan generation unit is adapted to generate an operation plan for the boiling unit on the basis of hot water supply load data of one of the plurality of groups generated by the hot water supply load data analysis unit, and having the maximum occurrence frequency, and the operation plan correction unit is adapted to select the hot water supply load data having the minimum error from the obtained hot water supply load result at the predetermined day after start of operation based on the operation plan, and to generate the subsequent operation plan at the predetermined day on the basis of the selected hot water supply load data. - a hot water storage tank that is adapted to store water; - a boiling unit that is a heating source that is adapted to heat the water stored in the hot water storage tank; and - a controller that is adapted to determine an amount of heat to be generated by the boiling unit, for each time slot by calculating a hot water supply load pattern that is typical for the user, in order to heat the water stored in the hot water storage tank, - a data measurement unit that measures a water temperature and a flow rate; - a hot water supply load data storage unit that is adapted to store hot water supply load data generated on the basis of at least a water temperature of water flowing into the hot water storage tank and a water temperature and a flow rate of water flowing out from the hot water storage tank, for a plurality of days; - a hot water supply load data analysis unit that is adapted to analyze the hot water supply load data for the plurality of days stored in the hot water supply load data storage unit; - an operation plan generation unit that is adapted to predict a hot water supply load for a predetermined day ahead of the plurality of days stored in the hot water supply load data storage unit, on the basis of the analysis by the hot water supply load data analysis unit, and to generate an operation plan for the boiling unit at the predetermined day on the basis of a result of prediction; and - an operation plan correction unit that, after start of operation based on the operation plan, is adapted to predict a subsequent hot water supply load at the predetermined day on the basis of an obtained hot water supply load result at the predetermined day, and to change the subsequent operation plan at the predetermined day generated by the operation plan generation unit, on the basis of the hot water supply load predicted again and a remaining amount of stored hot water in the hot water storage tank, and wherein the hot water supply load data analysis unit is adapted to classify the hot water supply load data for the plurality of days stored in hot water supply load data storage unit, into a plurality of groups, the operation plan generation unit is adapted to generate an operation plan for the boiling unit on the basis of hot water supply load data of one of the plurality of groups generated by the hot water supply load data analysis unit, and having the maximum occurrence frequency, and the operation plan correction unit is adapted to select the hot water supply load data having the minimum error from the obtained hot water supply load result at the predetermined day after start of operation based on the operation plan, and to generate the subsequent operation plan at the predetermined day on the basis of the selected hot water supply load data.