NOVELTY - A photoelectrochemical-reaction apparatus (10) comprises a photovoltaic layer (11) which has surface (S1) and surface (S2), an oxidation electrode layer (12) which is electrically connected to the surface (S1) of the photovoltaic layer, a reduction electrode layer (13) which is electrically connected to the surface (S2) of the photovoltaic layer, an electrolyte solution (14a) which includes water, an electrolyte solution (14b) which includes water and/or carbon dioxide, and a porous layer (16) which is in contact with electrolyte solution (14a) or electrolyte solution (14b).    USE - Photoelectrochemical-reaction apparatus is used for conversion of light to chemical substance.    ADVANTAGE - The photoelectrochemical-reaction apparatus enables efficient conversion of light with high conversion efficiency into storable and transportable chemical substance which has high availability.    DETAILED DESCRIPTION - A photoelectrochemical-reaction apparatus comprises a photovoltaic layer which has surface (S1) and surface (S2) which are mutually opposite and brings charge separation by energy of the light irradiated to the surface (S1) or the surface (S2), an oxidation electrode layer which is electrically connected to the surface (S1) of the photovoltaic layer, and which oxidizes water, a reduction electrode layer which is electrically connected to the surface (S2) of the photovoltaic layer, and which reduces water and/or carbon dioxide, an electrolyte solution (14a) which includes water and is supplied to the oxidation electrode layer, an electrolyte solution (14b) which includes water and/or carbon dioxide and which is supplied to reduction electrode layer, and a porous layer which is in contact with electrolyte solution (14a) or electrolyte solution (14b), and has pores for passing the reaction product of oxidation or reduction and refines the products by giving temperature gradient.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of photoelectrochemical-reaction apparatus.    Photoelectrochemical-reaction apparatus (10)    Photovoltaic layer (11)    Oxidation electrode layer (12)    Reduction electrode layer (13)    Electrolyte solution (14,14a,14b)    Porous layer (16)    Flow path (17)