A method of processing an object using a plasma processing apparatus is provided. The plasma processing apparatus includes a stage on which the object is placed in a chamber, an outer peripheral member disposed around the stage, and a first power supply configured to apply voltage to the outer peripheral member. The method includes a step of exposing the object to a plasma containing a precursor having a deposition property, while applying voltage from the first power supply to the outer peripheral member. In applying voltage to the outer peripheral member, a status of a deposition film containing carbon that is deposited on the outer peripheral member is monitored, and the voltage applied to the outer peripheral member is controlled based on the monitored status of the deposition film.