A substrate processing apparatus for cleaning and drying a substrate under processing, including supplying a cleaning liquid onto the substrate under processing to form a cleaning liquid layer, supplying a gas onto the substrate under processing to partially remove the cleaning liquid layer and thus generate a first dry region on the substrate under processing, expanding the first dry region to generate a second dry region by controlling the movement speed of the boundary between the cleaning liquid layer and the first dry region to be less than or equal to a predetermined speed, and further expanding the second dry region to generate a third dry region.