PURPOSE: To enable the measurement of moisture with higher accuracy in a short time as adsorbed on various samples immediately after a surface treatment by providing a treating function in a measuring device for forming various surface conditions on the surface of the samples by a fully closed system to shut off the sample from the atmospheric air up the measurement of the amount of water from the surface treatment.

CONSTITUTION: Valves 11-14 are opened to introduce various gases and solutions for a surfaces treatment and a desired treating temperature is kept with a heater 5 and a temperature controller 7 to perform a surface treatment. Then, a gas containing moisture is introduced to make the moisture adsorb and the valves 11-14 are closed. When the amount of the moisture is measured, a medical fluid container 1 is heated 4 and 6 up to an aimed temperature and with a value 15 opened, the gas corresponding to the vapor pressure of the medical fluid is liquefied with a condenser 8 and then, a value 16 is opened to send the medical fluid to an electroconductivity meter 3 via a value 17, a control tube 9 and a valve 18 controlling 2 the flow rate of the medical fluid. Then, the electroconductivity becomes constant, the valves 17 and 18 are closed while the valves 19 and 12 are opened to introduce the medical fluid to a sample tube 10 and the moisture adsorbed is dissolved to be sent to the electroconductivity meter 3.