In a depth dose measuring device, a light is outputted from an end surface of a block-type detector (202) formed by tying a plurality of scintillation fibers in a bundle, a spectroscope (204) is used to disperse the light so as to measure an amount of light having a wavelength corresponding to an emission spectrum of the scintillation fibers, a picture measuring device (205) and a picture processing device (206) calculate an emission distribution of only a scintillation light depending upon an emission distribution in which the scintillation light and a Cerenkov light are mixed, and a result is displayed on a display device (207).