To balance the pressures of two kinds of produced gases through simplified constitution, more safely and more efficiently at lower cost.

If the pressure of produced gas guided to a left partition chamber 3 increases for some reason, a thin-film body 2 receives the gas pressure to flex and swell toward a right partition chamber 4, thereby increasing the capacity of the left partition chamber 3. As the thin-film body swells, the capacity of the right partition chamber 4 decreases. As the capacity varies, the pressure in the left partition chamber 3 becomes small and the pressure of the right partition chamber 4 becomes large according to the Boyle's law. The pressures of the gases in both the partition chambers 3 and 4 can be balanced again to a previously set pressure.