A photodetection device comprising: a photodetector comprising: N photodetection pixels arranged one-dimensionally or two-dimensionally and each for generating a detection signal in response to incidence of light, wherein N is an integer of 2 or more; and a single output terminal for outputting the detection signal generated in each of the N photodetection pixels, a time waveform measurement unit for measuring the time waveform of the detection signal output from the output terminal of the photodetector (50, 50A, 50B); and an analysis unit for obtaining a time constant indicating the time waveform of the detection signal based on a measurement result by the time waveform measurement unit, wherein each of the N photodetection pixels includes an avalanche photodiode operating in Geiger mode, and a quenching resistor connected in series to the avalanche photodiode, the N photodetection pixels are configured to output detection signals having time waveforms different from each other, the quenching resistors of the N photodetection pixels have resistance values different from each other, the time waveform measurement unit includes: a first comparator for comparing the detection signal with a first threshold voltage and outputting a first digital signal having a first time width corresponding to a time during which a voltage value of the detection signal exceeds the first threshold voltage; a first time width measurement device for measuring the first time width of the first digital signal; a second comparator for comparing the detection signal with a second threshold voltage different from the first threshold voltage and outputting a second digital signal having a second time width corresponding to a time during which the voltage value of the detection signal exceeds the second threshold voltage; and a second time width measurement device for measuring the second time width of the second digital signal, and wherein the analysis unit obtains the time constant of the detection signal based on the first time width and the second time width. a photodetector comprising: N photodetection pixels arranged one-dimensionally or two-dimensionally and each for generating a detection signal in response to incidence of light, wherein N is an integer of 2 or more; and a single output terminal for outputting the detection signal generated in each of the N photodetection pixels, N photodetection pixels arranged one-dimensionally or two-dimensionally and each for generating a detection signal in response to incidence of light, wherein N is an integer of 2 or more; and a single output terminal for outputting the detection signal generated in each of the N photodetection pixels, a time waveform measurement unit for measuring the time waveform of the detection signal output from the output terminal of the photodetector (50, 50A, 50B); and an analysis unit for obtaining a time constant indicating the time waveform of the detection signal based on a measurement result by the time waveform measurement unit, wherein each of the N photodetection pixels includes an avalanche photodiode operating in Geiger mode, and a quenching resistor connected in series to the avalanche photodiode, the N photodetection pixels are configured to output detection signals having time waveforms different from each other, the quenching resistors of the N photodetection pixels have resistance values different from each other, the time waveform measurement unit includes: a first comparator for comparing the detection signal with a first threshold voltage and outputting a first digital signal having a first time width corresponding to a time during which a voltage value of the detection signal exceeds the first threshold voltage; a first time width measurement device for measuring the first time width of the first digital signal; a second comparator for comparing the detection signal with a second threshold voltage different from the first threshold voltage and outputting a second digital signal having a second time width corresponding to a time during which the voltage value of the detection signal exceeds the second threshold voltage; and a second time width measurement device for measuring the second time width of the second digital signal, and wherein the analysis unit obtains the time constant of the detection signal based on the first time width and the second time width. a first comparator for comparing the detection signal with a first threshold voltage and outputting a first digital signal having a first time width corresponding to a time during which a voltage value of the detection signal exceeds the first threshold voltage; a first time width measurement device for measuring the first time width of the first digital signal; a second comparator for comparing the detection signal with a second threshold voltage different from the first threshold voltage and outputting a second digital signal having a second time width corresponding to a time during which the voltage value of the detection signal exceeds the second threshold voltage; and a second time width measurement device for measuring the second time width of the second digital signal, and wherein the analysis unit obtains the time constant of the detection signal based on the first time width and the second time width.