This study performed thermochemical CO2 splitting experiment using vertical tubular furnace in the case of high-temperature conditions including a reduction temperature of 1500 ℃ - 1600 ℃. The experiment mimicked a reacting flow and its heat transfer inside a tubular reactor with high-temperature solar heat created by a sun concentrator. Experimentally, a foam device of ceria (CeO2) was reduced to release O2 at temperature of 1400 ℃ or higher and the same device deprived oxygen from a stream of CO2 to produce CO at 1400℃ or below. The experiment revealed that the production of CO became 50 % larger as the temperature at reduction increased from 1500 ℃ to 1600 ℃. Also, it was revealed that the effects from temperature at oxidation was not essential when the temperature was higher than 700 ℃. The highest level of production of CO reached 7.0 mL/g Ceria at 1600 ℃ of reduction temperature. As to the gas concentration, percentage of CO exceeded 30% when the experiment used three pieces of the foam device whose total weight was 133 g. The experimental results were compared with and they were found to agree with the equilibrium theory where the partial pressure of oxygen at the reduction step was assigned at 1.0 x 10-4 atm. This quantity was cited at the numerical condition for the system analysis of demonstration plant. The analysis indicated that the overall efficiency from solar to the combustion heat of CO can be higher than 10 % with the recuperation of exhaust heat of released gas and reactive material, where a demonstration plant was assumed. Also, it was indicated that the efficiency can be 20 - 30 % if recuperating the exhaust heat of oxidation and released oxygen and surplus heat of reactive material, assuming a commercial plant.