1. A plasma processing method for monitoring information on a plasma processing in a processing apparatus which generate plasma in an air-tight processing chamber to plasma-process objects to be processed, the plasma processing method comprising: a data colleting step of collecting detection values detected for each of the objects from a plurality of detection devices disposed in the processing apparatus upon the plasma processing; a compensating step of compensating the detection values from the detection devices in respective sections that are defined whenever a maintenance of the processing apparatus is performed; and an analysis processing step of performing a multivariate analysis by using as analysis data the compensated detection values and monitoring information on the plasma processing based on the analysis results.