It is an object to carry out a chemical treatment for a peripheral edge part of a substrate while suppressing an amount of consumption of a processing liquid and a time required for processing. In order to achieve the object, a substrate processing device injects heating steam to a peripheral edge part of a substrate to heat the peripheral edge part when carrying out a chemical treatment for the peripheral edge part of the substrate while rotating the substrate in a substantially horizontal posture. Moreover, the substrate processing device injects a gas from above the substrate toward a predetermined injection target region defined within a range surrounded by a rotating track of the peripheral edge part of the substrate in an upper surface of the substrate, thereby generating, on the substrate, a gas flow which flows from the injection target region toward the peripheral edge part of the substrate.