Provided are a processing method and a processing apparatus in which a concentration of a solid content of a development fatigue liquid is low and a moisture content of a discharged solid substance is small. The processing method is a method for removing a first solid substance having a smaller specific gravity than the washout liquid and a second solid substance having a larger specific gravity than the washout liquid from a development fatigue liquid including a solid substance generated by removal of a non-exposed portion of a photosensitive resin plate that has been exposed in an image shape by development using the washout liquid. The method includes a first step of centrifugally separating the first solid substance and the second solid substance included in the development fatigue liquid in a rotating container, accumulating the second solid substance on an inner wall of the container, and accumulating the first solid substance on a holding member provided in the container, a second step of discharging the development fatigue liquid from the container in a state in which the first solid substance accumulated on the holding member is held on the holding member, and a third step of rotating the container, thereby removing the first solid substance held on the holding member from the holding member.