In closed environments such as space stations, it is necessary to eliminate CO2 produced by the metabolisms of crew members, for their life support, and to regenerate the air by supplying O2 to make up for the deficiency. If humans are to be in space only a short time, it is in general advantageous to adsorb CO2 with lithium hydroxide, and to supply O2 from tanks. But when the stay in space is long, it is essential to establish a highly reliable and energy-efficient system to recover CO2 in high concentrations and regenerate O2 from this recovered CO2 Fig. 1 shows the system presently conceived, which is roughly divided into the following processes: A process that removes and concentrates CO2 from the air; a CO2 reduction process that separates carbon from CO2 and obtains water; and a water electrolysis process that decomposes water electrically and recovers O2. The process deemed most promising both in terms of low energy consumption and reliability for removing and concentrating CO2. In this process, solid amine removes CO2 produced by human metabolisms, desorbs it, then separates and concentrates CO2 of high purity.Bosch reaction, which proceeds at comparatively low temperatures, is thought to be advantageous for the CO2 reduction process, and using a solid electrolyte is advantageous for the water electrolysis process.This research involved several tests, and simulated analysis for these processes to examine the optimum conditions for the effective operation of the system.