A system comprising: a chamber which is surrounded by a heat-insulating part, said chamber defining a measurement space which is a space inside the chamber and an external space which is a space outside the chamber; and a dew-point instrument configured to measure a dew-point of the measurement space, the dew-point instrument comprising: a main body part configured by a heat pipe or a meandering capillary tube type heat pipe or an oscillating heat pipe, said main body part being configured to encapsulate a working fluid therein and to cause a heat-pipe phenomenon and is disposed across the measurement space and the external space that is spaced from the measurement space by the heat-insulating part and has a temperature lower than that of the measurement space; and first temperature deriving means configured to derive a temperature of the main body part in a section where the working fluid evaporates, said section where the working fluid evaporates corresponds to a part of the main body part which is inserted in the chamber; characterized in that: the first temperature deriving means is attached to a surface of a section of the main body part which is disposed inside the measurement space, said section being a section where the working fluid in liquid form accumulates when the heat-pipe phenomenon is completely caused in the main body part, said section where the working fluid in liquid form accumulates corresponds to the part of the main body part which is inserted in the chamber. a chamber which is surrounded by a heat-insulating part, said chamber defining a measurement space which is a space inside the chamber and an external space which is a space outside the chamber; and a dew-point instrument configured to measure a dew-point of the measurement space, the dew-point instrument comprising: a main body part configured by a heat pipe or a meandering capillary tube type heat pipe or an oscillating heat pipe, said main body part being configured to encapsulate a working fluid therein and to cause a heat-pipe phenomenon and is disposed across the measurement space and the external space that is spaced from the measurement space by the heat-insulating part and has a temperature lower than that of the measurement space; and first temperature deriving means configured to derive a temperature of the main body part in a section where the working fluid evaporates, said section where the working fluid evaporates corresponds to a part of the main body part which is inserted in the chamber; a main body part configured by a heat pipe or a meandering capillary tube type heat pipe or an oscillating heat pipe, said main body part being configured to encapsulate a working fluid therein and to cause a heat-pipe phenomenon and is disposed across the measurement space and the external space that is spaced from the measurement space by the heat-insulating part and has a temperature lower than that of the measurement space; and first temperature deriving means configured to derive a temperature of the main body part in a section where the working fluid evaporates, said section where the working fluid evaporates corresponds to a part of the main body part which is inserted in the chamber; characterized in that: the first temperature deriving means is attached to a surface of a section of the main body part which is disposed inside the measurement space, said section being a section where the working fluid in liquid form accumulates when the heat-pipe phenomenon is completely caused in the main body part, said section where the working fluid in liquid form accumulates corresponds to the part of the main body part which is inserted in the chamber.