To provide a separation, recovery and treatment apparatus of carbon dioxide in the atmosphere which when generating power by a biomass can recover and treat the carbon dioxide efficiently and without diffusing into the atmosphere, and can contribute to the reduction and cut of carbon dioxide in the atmosphere.

The apparatus includes a device (2) for generating a biogas from a biomass (1), a power generating device (3, 3A) for generating power using the biogas as a fuel, a mechanism (12) for supplying oxygen to the exhaust gas from the power generating device (3, 3A) so that the composition of the exhaust gas is composed only of carbon dioxide and water, a mechanism (5) for separating the water condensed by cooling the exhaust gas composed only of carbon dioxide and water, a water supplying mechanism (40) for supplying the cleaned water produced from the separated condensed water as biomass dilution water, and an oxygen production device (35) for producing oxygen by using the electric power generated from the power generating device.