A photocatalyst electrode decomposes water with light to generate gas. The photocatalyst electrode has a laminate including a substrate, a conductive layer provided on a surface of the substrate, and a photocatalyst layer provided on a surface of the conductive layer, and a first co-catalyst electrically connected to the photocatalyst layer. The light is incident from the surface side of the photocatalyst layer of the laminate, and in a case where a region where the light is incident on the surface of the photocatalyst layer and above the surface is defined as a first region and the region other than the first region is defined as a second region, the first co-catalyst is provided at least in the second region. The first co-catalyst and the photocatalyst layer are electrically connected to each other by at least one of a transparent conductive layer provided on the surface of the photocatalyst layer or a wiring line.