A substrate processing apparatus can prevent photo-corrosion of, e.g., copper interconnects due to exposure of a surface to be processed of a substrate to light, and can perform processing, such as cleaning, of a substrate surface while preventing photo-corrosion of, e.g., copper interconnects due to exposure to light. The substrate processing apparatus includes a plurality of processing areas housing therein processing units which have been subjected to light shielding processing; and at least one transfer area housing therein a transfer robot and disposed between two adjacent ones of the plurality of processing areas. A light shielding wall is provided between the transfer area and each of the two adjacent processing areas, and a light-shielding maintenance door is provided for the front opening of the transfer area. The processing units are coupled to the light shielding walls in a light-shielding manner.