A radiation detection device includes a scintillator, a photodetector for detecting scintillation light from the scintillator and outputting a detection signal, a first comparator for comparing the detection signal with a first threshold voltage V1 and outputting a signal having a first time width T1, a first time width measurement device for measuring the first time width T1, a second comparator for comparing the detection signal with a second threshold voltage V2 and outputting a signal having a second time width T2, a second time width measurement device for measuring the second time width T2, and an analysis unit for obtaining a time constant τ indicating a time waveform of the detection signal based on the first and second time widths T1 and T2.