A heat transfer method using a heat transfer system, the heat transfer system including: a heat source unit in which heat is configured to be exchanged between a heat transfer medium and a heat source, a utilization unit in which heat is configured to be exchanged between the heat transfer medium and a temperature adjustment target, a first flow path that connects the heat source unit and the utilization unit and through which the heat transfer medium is configured to flow from the heat source unit to the utilization unit, and a second flow path that connects the heat source unit and the utilization unit and through which the heat transfer medium is configured to flow from the utilization unit to the heat source unit, the method comprising: controlling the temperature of the heat transfer medium flowing through the first flow path to be lower than the temperature of the heat transfer medium flowing through the second flow path to transfer cold heat from the heat source unit to the utilization unit; using, as the heat transfer medium, inorganic hydrate slurry in which an inorganic hydrate that absorbs heat when dissolved in water is mixed with water; controlling the heat transfer system so that a temperature of the heat transfer medium flowing through the first flow path and a temperature of the heat transfer medium flowing through the second flow path become equal to or below a melting point of the inorganic hydrate; and making an amount of the inorganic hydrate dissolved per unit mass of water in the heat transfer medium flowing through the first flow path different from an amount of the inorganic hydrate dissolved per unit mass of water in the heat transfer medium flowing through the second flow path wherein a diameter of a pipe forming the first flow path is larger than a diameter of a pipe forming the second flow path. a heat source unit in which heat is configured to be exchanged between a heat transfer medium and a heat source, a utilization unit in which heat is configured to be exchanged between the heat transfer medium and a temperature adjustment target, a first flow path that connects the heat source unit and the utilization unit and through which the heat transfer medium is configured to flow from the heat source unit to the utilization unit, and a second flow path that connects the heat source unit and the utilization unit and through which the heat transfer medium is configured to flow from the utilization unit to the heat source unit, the method comprising: controlling the temperature of the heat transfer medium flowing through the first flow path to be lower than the temperature of the heat transfer medium flowing through the second flow path to transfer cold heat from the heat source unit to the utilization unit; using, as the heat transfer medium, inorganic hydrate slurry in which an inorganic hydrate that absorbs heat when dissolved in water is mixed with water; controlling the heat transfer system so that a temperature of the heat transfer medium flowing through the first flow path and a temperature of the heat transfer medium flowing through the second flow path become equal to or below a melting point of the inorganic hydrate; and making an amount of the inorganic hydrate dissolved per unit mass of water in the heat transfer medium flowing through the first flow path different from an amount of the inorganic hydrate dissolved per unit mass of water in the heat transfer medium flowing through the second flow path wherein a diameter of a pipe forming the first flow path is larger than a diameter of a pipe forming the second flow path. controlling the temperature of the heat transfer medium flowing through the first flow path to be lower than the temperature of the heat transfer medium flowing through the second flow path to transfer cold heat from the heat source unit to the utilization unit; using, as the heat transfer medium, inorganic hydrate slurry in which an inorganic hydrate that absorbs heat when dissolved in water is mixed with water; controlling the heat transfer system so that a temperature of the heat transfer medium flowing through the first flow path and a temperature of the heat transfer medium flowing through the second flow path become equal to or below a melting point of the inorganic hydrate; and making an amount of the inorganic hydrate dissolved per unit mass of water in the heat transfer medium flowing through the first flow path different from an amount of the inorganic hydrate dissolved per unit mass of water in the heat transfer medium flowing through the second flow path wherein a diameter of a pipe forming the first flow path is larger than a diameter of a pipe forming the second flow path.