PURPOSE: To decrease the number of photoelectric converters, by using the photoelectric converters in common for the number of spatially sampled values of radiation.

CONSTITUTION: Three adjacent scintillators 11, 12, and 13 among plural scintillators are connected to two photoelectric converters 31 and 32 through light guides 21W24. The output of the scintillators 11 and 13 are sent to the converters 31 and 32, as they are, and the half and other of the output of the scintillator 12 are sent to the converters 31 and 32 respectively. The outputs of the converters 31 and 32 are sent to peak discriminators 51W53 through amplifiers 41 and 42 and an adder 43. When the lower limit values of the discriminators 51 and 53 are set, for example, to 70%, only output pulses of the scintillators 11 and 13 are detected. The discriminator 52 is inhibited from generating its output only when the discriminators 51 and 53 generate outputs and generates the output corresponding to the scintillator 12.