According to one embodiment, a photochemical reaction system comprises a CO 2 production unit, a CO 2 absorption unit, and a CO 2 reduction unit. The CO 2 reduction unit comprises a laminated body and an ion transfer pathway. The laminated body comprises an oxidation catalyst layer producing O 2 and H + by oxidizing H 2 O, a reduction catalyst layer producing carbon compounds by reducing CO 2 absorbed by the CO 2 absorption unit, and a semiconductor layer formed between the oxidation catalyst layer and the reduction catalyst layer and develops charge separation with light energy. The ion transfer pathways make ions move between the oxidation catalyst layer side and the reduction catalyst layer side.
