To provide Zinc Sulfide activated with Silver (ZnS:Ag) based fluorescent material for detecting particle beams, having lower gamma-ray sensitivity and providing lower afterglow, and being specialized for the purpose of detecting particle beams, and its manufacturing method. Zinc Sulfide activated with Silver (ZnS:Ag) based fluorescent material for detecting particle beams emits fluorescence with wavelengths from 320 nm to 580 nm in response to alpha-ray irradiation, and has a fluorescence spectrum with a peak wavelength from 395 nm to 410 nm.