Abstract: A household wastewater purification system includes a first treatment tank having a household wastewater inlet in an upper part thereof, a photocatalytic decomposition treatment device having a photocatalytic material at least a part of which lies above the water surface, and an anaerobic treatment device. A second treatment tank is adjacent to the first treatment tank and isolated therefrom by a partition wall except a lower part thereof that is communicated with a lower part of the first treatment tank. The second treatment tank has an aerobic treatment device therein and a purified water outlet in an upper part thereof. A light-introducing part is provided above the first treatment tank.