In a thermomechanical measuring device and a thermogravimetry device, partition walls are provided in two sections such that two kinds of atmospheric gasses, which have passed a sample chamber and a detector chamber, respectively, do not flow back, and a thermally insulated gas mixing chamber is manufactured anew in the middle of the sample chamber and the detector chamber to make it possible to dilute a reactive gas and a water vapor gas having a high partial pressure. Consequently, it is possible to prevent moisture concentration to reduce an influence of water drops even in a high temperature and high humidity state at the time of humidity control and measurement.