Provided is a substrate processing apparatus and substrate processing method capable of processing a substrate by using plasma, the substrate processing apparatus including a process chamber providing an internal space where a substrate is processed, a spin chuck serving as a lower electrode, supporting the substrate in the internal space of the process chamber, and rotating the supported substrate, and a plasma generation unit mounted in an upper portion of the process chamber to face the spin chuck, including a discharge space where an upper electrode is provided, generating plasma by using a process gas supplied from outside, linearly ejecting the plasma onto the substrate rotated by the spin chuck, and controlling a density of the plasma to change along an extension direction of the linearly ejected plasma.