A muon monitoring system for particle radiation therapy includes: a shield for a selective passing, by eliminating particles and radiation produced due to the high energy particles and radiation pulses, of the delay positrons emitted due to decay of muons stopped at a position corresponding to the Bragg peak position; a positron detector for detecting positrons from a designated direction and detecting the delay positrons passed through the shield opening by each of positron detecting plates for providing information of positron produced positions and time of delay simultaneous signals; and a control/analysis apparatus generating a delay signal at a timing delayed by a predetermined time period from a completion of irradiation of the high energy particle radiation pulses, and performing a process to generate μSR signals segmented for each positron generating position by analyzing detected results obtained by operating the positron detector for a predetermined number of times.