Provided are a photocatalyst electrode, an artificial photosynthesis module, and an artificial photosynthesis device that have low electrical resistance, even in a case where the area is increased, in a case where a transparent conductive layer is used. The photocatalyst electrode is a photocatalyst electrode that has a substrate, a transparent conductive layer, a photocatalyst layer, and a linear metal electrical conductor, and splits water with light to produce a gas. The substrate, the transparent conductive layer, and the photocatalyst layer are laminated in this order, and the linear metal electrical conductor is in contact with the transparent conductive layer. The artificial photosynthesis module has the oxygen evolution electrode that splits the water with the light to produce oxygen, and a hydrogen evolution electrode that splits the water with the light to produce hydrogen. The oxygen evolution electrode and the hydrogen evolution electrode are disposed in series in a traveling direction of the light. At least one of the oxygen evolution electrode or the hydrogen evolution electrode has the configuration of the above-described photocatalyst electrode. The artificial photosynthesis device has the artificial photosynthesis module, and circulates and utilizes water.