PURPOSE: To make pressure and steam pressure in a test tank controllable simply and accurately by interconnecting a saturated water tank, forcing air into saturated steam pressure by way of making water and inflow air at the preset temperature contact with each other, with this test tank.

CONSTITUTION: A desired flow rate of air is fed to a saturated tank 1 from its lower part. This air passes through a filter 2 and comes to fine bubbles, passing through a water current 3 at the preset temperature in the underwater, and finally it is reached to an upper space of the saturated tank 1. This air passes through a pipe 5, joining with a corrosive gas from a pipe 6, coming into a test tank 8. Here, a temperature in the saturated tank 1 is kept constant by a constant tenperature water tank, while the air run past the saturated tank 1 has constant steam pressure to be determined by the temperature of the saturated tank 1, therefore it comes 9.206mmHg, 92.596mmHg each at temperatures of 10°C and 50°C, by way of example. As for the air, if it is preset so as to be saturated at the maximum flow rate and temperature, it is fully saturated with water vapor, and a fact that temperature control over the water tank 4 is set to ±0.1° is not so hard to be done. With this constitution, temperature and steam pressure in the test tank 8 can be controlled simply and accurately.