A processing apparatus includes: a light emission unit configured to emit light to a surface of a particle dispersed liquid applied to a base material, the particle dispersed liquid having particles dispersed in a solvent; a reflected light amount monitoring unit configured to detect an amount of the light reflected, and monitor a temporal variation of the detected value; and a condition adjustment unit configured to adjust a condition for a particle securing process, the particle securing process being performed to remove the solvent and secure the particles onto the base material, wherein, when the temporal variation falls within a predetermined range after the value has reached an extreme value, securing of the particles is determined to have been completed.