A plasma processing device performing etching processing to a sample disposed in a processing chamber disposed in a vacuum vessel by using plasma formed in the processing chamber includes a light detector, a component detector, and a determination unit. The light detector detects light intensity of a plurality of wavelengths from the inside of the processing chamber at a plurality of times during the sample processing. The component detector detects, by using a result of a principal component analysis of time-series data, a highly correlated component between the time-series data of a plurality of the wavelengths at a certain time in a plurality of the times obtained from output of the light detector. The determination unit determines an amount or an end point of the etching processing based on a change in light intensity of at least one of a plurality of the wavelengths detected by using the time-series data from which the highly correlated component is removed.