A heat transport device comprising: a circulation path unit in which a heat recovery unit that vaporizing a heat transport medium and a condensation unit that condenses the heat transport medium vaporized in the heat recovery unit are incorporated, and which has a vacuum state; a branch path unit which branches from the circulation path unit, and in which a valve capable of controlling flow is incorporated; and a first control unit configured to open and close the valve in a state in which pressure in the circulation path unit is higher than a predetermined pressure (α) when it is detected or estimated that the circulation path unit sucks air, characterized in that: the heat transport device further comprises a reserve tank that stores, in a liquid phase, heat transport medium with which the circulation path unit is to be replenished, the branch path unit being connected to the reserve tank so as to have an opening located in a position lower than a height of a liquid level that is to be at least ensured in the reserve tank; and wherein the heat transport device further comprises a replenishment quantity calculation unit that calculates a quantity of heat transport medium with which the circulation path unit should be replenished from the reserve tank, and a second control unit configured to open and close the valve in accordance with the quantity of heat transport medium calculated by the replenishment quantity calculation unit in a state in which the pressure in the circulation path unit is lower than the predetermined pressure after the first control unit opens and closes the valve. a circulation path unit in which a heat recovery unit that vaporizing a heat transport medium and a condensation unit that condenses the heat transport medium vaporized in the heat recovery unit are incorporated, and which has a vacuum state; a branch path unit which branches from the circulation path unit, and in which a valve capable of controlling flow is incorporated; and a first control unit configured to open and close the valve in a state in which pressure in the circulation path unit is higher than a predetermined pressure (α) when it is detected or estimated that the circulation path unit sucks air, characterized in that: the heat transport device further comprises a reserve tank that stores, in a liquid phase, heat transport medium with which the circulation path unit is to be replenished, the branch path unit being connected to the reserve tank so as to have an opening located in a position lower than a height of a liquid level that is to be at least ensured in the reserve tank; and wherein the heat transport device further comprises a replenishment quantity calculation unit that calculates a quantity of heat transport medium with which the circulation path unit should be replenished from the reserve tank, and a second control unit configured to open and close the valve in accordance with the quantity of heat transport medium calculated by the replenishment quantity calculation unit in a state in which the pressure in the circulation path unit is lower than the predetermined pressure after the first control unit opens and closes the valve. the heat transport device further comprises a reserve tank that stores, in a liquid phase, heat transport medium with which the circulation path unit is to be replenished, the branch path unit being connected to the reserve tank so as to have an opening located in a position lower than a height of a liquid level that is to be at least ensured in the reserve tank; and wherein the heat transport device further comprises a replenishment quantity calculation unit that calculates a quantity of heat transport medium with which the circulation path unit should be replenished from the reserve tank, and a second control unit configured to open and close the valve in accordance with the quantity of heat transport medium calculated by the replenishment quantity calculation unit in a state in which the pressure in the circulation path unit is lower than the predetermined pressure after the first control unit opens and closes the valve.