A photoelectrochemical cell (1) includes an electrolyte container (3) containing an ionic liquid (2), and a partitioning membrane (4) dividing an interior of the electrolyte container (3) into two being a CO2 capturing chamber (7) and a CO2 releasing chamber (8), having side walls opposing each other, with the partitioning membrane (4) in between, either as a carbon electrode (5) and the other as a photoelectrode (6). A redox mediator (B) has different bonding forces to carbon dioxide, as it appears as an oxidant Box and a reductant Bred, of which that one which has a greater bonding force serves as an intermediary chemical species carrying carbon dioxide to one of the paired electrodes (5, 6). Over the CO2 releasing chamber (10), an upper wall portion (10) is formed, which has a CO2 take-out port (10A) formed therein, for making use of oxidation and reduction of the redox mediator to achieve separation and concentration of carbon dioxide, converting photo energy of sunlight into electric power.