In a closed type thermal power generation plant, the fuel is supplied in the combustor and burnt therein in the presence of oxygen, instead of air. The combustion gas mainly including water and carbon dioxide is delivered from the combustor into the turbine. A turbine exhaust gas is fed into the waste heat boiler to carry out heat exchanging operation therein and an exhaust gas mainly including water component and carbon dioxide from the waste heat boiler is fed into the condenser. The gas component mainly including the carbon dioxide is separated from the condensate in the water-gas separator and may be fed into the combustor in a compressed state, or the separated gas component may be recovered externally to the plant without emitting the same into the atmosphere. The separated condensate is fed into the waste heat boiler to be subjected to heat exchanging operation therein to generate superheated steam which is to be fed into the combustor, or may be recovered externally.Further, a steam turbine may be connected to the waste heat boiler and generator. A condensor may then be connected to the steam turbine and waste heat boiler so that the steam turbine, condenser and waste heat boiler constitute a closed cycle.