PURPOSE: To perform effective fermentation control by making the waste gases from plural juxtaposed fermentation vessels changeable to releasing to the atmosphere and to suction to the measuring instrument side by operating solenoid valves, measuring the concns. of CO2 and O2 in the waste gases with measuring instruments and detecting fermentation characteristics.

CONSTITUTION: The gas release pipes 4 of plural juxtaposed fermentation vessels 1 which perform aerobic fermentation by supplying and discharging of gases are connected to one gas release pipe A via the solenoid valves SV1WSVn provided to these respectively so that the fermentation gases produced in the vessels 1 are released into the atmosphere. At this time, the waste gases are introduced through a suction pipe G into a CO2 measuring device I and an O2 measuring device J from arbitrary vessel 1 for a constant time by opening and closing the valves SV1WSVn selectively and operating a pump P. In this way, the concns. of CO2 and O2 in the waste gases of the vessels 1 are measured and fermentation characteristics are detected.