PURPOSE: To make it possible to measure the capability of a product under test accurately based on the amount of dew condensation, dew-point temperature and flow rate which are not changed under pressure by providing a control device which detects the temperature with a temperature detecting means and keeps the specified temperature and humidity for heating and moisturizing means.

CONSTITUTION: Air from a filter 6 is detected with a temperature detecting means 15 and a humidity detecting means 16. The results are compared with temperature and humidity which are inputted into a temperature/humidity controller 18 beforehand. The operations of each heater 4 and each moisturizing device 5 are controlled. The detected temperature and humidity are recorded in a recorder 20. The dry air which is outputted through the air outlet of an air dehumidifier 8 is measured in the vicinity of the outlet. The dew-point temperature, the temperature and the pressure are recorded in the recorder 20. The flow rate per unit time of the air from the air dehumidifier 8 is measured with a flowmeter 10 or 13 and recorded in the recorder 20. When the amount of the moisture which is removed in the air dehumidifier 8 is measured, the absolute humidity can be computed, and the capabilities of air apparatuses under pressure can be compared and collated.