A processing apparatus and a processing method for a semiconductor wafer, which allow stable end point detection, are provided. In the plasma processing apparatus or method in which a processing-target film layer of a film structure including a plurality of film layers formed in advance on a surface of a wafer mounted on a sample stage deployed within a processing chamber inside a vacuum vessel, by using plasma formed with the processing chamber, intensities of lights of a plurality of wavelengths are detected using data composed of results of reception of lights during a plurality of different time-intervals by an optical receiver which receives lights of the plurality of wavelengths from an inside of the processing chamber while processing is going.