Disclosed is a substrate processing apparatus including a chamber having a processing space inside, a support unit that supports a substrate in the processing space, a gas supply unit that supplies gas into the processing space, a plasma source that generates plasma from the gas supplied into the processing space, and a detection unit that is provided in a sidewall of the chamber and that measures an impedance change to detect a degree of adsorption of particles on an inner wall of the chamber or a surface of a part that is exposed to the processing space.