A radiation position detector comprising: a scintillator array including a plurality of scintillators on which radiation is incident; an optical detector array including a plurality of optical detectors corresponding one-to-one to the scintillators of the scintillator array; an AD conversion unit configured to convert each analog signal output from each optical detector of the optical detector array into a digital signal; and a position detection processing unit configured to specify a position of the scintillator on which the radiation is incident on the basis of the each digital signal obtained through the conversion by the AD conversion unit, wherein the each digital signal has at least time data corresponding to a time at which the radiation is incident, energy value data corresponding to a value of detected energy, and position data corresponding to an address of the scintillator in the scintillator array, and wherein the position detection processing unit includes: an energy comparison unit configured to compare, if there are two different digital signals having time data indicating the same time, energy value data of the two digital signals with an energy value of a Compton edge; and a position determination unit configured to determine that: when both energy values of the two digital signals are greater than the energy value of the Compton edge, the radiation is simultaneously incident on two scintillators corresponding to the position data of the two digital signals; when at least one of the energy values of the two digital signals is less than the energy value of the Compton edge, the address of the scintillator on which the radiation is incident is determined by comparing the energy values of the two digital signals. a scintillator array including a plurality of scintillators on which radiation is incident; an optical detector array including a plurality of optical detectors corresponding one-to-one to the scintillators of the scintillator array; an AD conversion unit configured to convert each analog signal output from each optical detector of the optical detector array into a digital signal; and a position detection processing unit configured to specify a position of the scintillator on which the radiation is incident on the basis of the each digital signal obtained through the conversion by the AD conversion unit, wherein the each digital signal has at least time data corresponding to a time at which the radiation is incident, energy value data corresponding to a value of detected energy, and position data corresponding to an address of the scintillator in the scintillator array, and wherein the position detection processing unit includes: an energy comparison unit configured to compare, if there are two different digital signals having time data indicating the same time, energy value data of the two digital signals with an energy value of a Compton edge; and a position determination unit configured to determine that: when both energy values of the two digital signals are greater than the energy value of the Compton edge, the radiation is simultaneously incident on two scintillators corresponding to the position data of the two digital signals; when at least one of the energy values of the two digital signals is less than the energy value of the Compton edge, the address of the scintillator on which the radiation is incident is determined by comparing the energy values of the two digital signals. an energy comparison unit configured to compare, if there are two different digital signals having time data indicating the same time, energy value data of the two digital signals with an energy value of a Compton edge; and a position determination unit configured to determine that: when both energy values of the two digital signals are greater than the energy value of the Compton edge, the radiation is simultaneously incident on two scintillators corresponding to the position data of the two digital signals; when at least one of the energy values of the two digital signals is less than the energy value of the Compton edge, the address of the scintillator on which the radiation is incident is determined by comparing the energy values of the two digital signals. when both energy values of the two digital signals are greater than the energy value of the Compton edge, the radiation is simultaneously incident on two scintillators corresponding to the position data of the two digital signals; when at least one of the energy values of the two digital signals is less than the energy value of the Compton edge, the address of the scintillator on which the radiation is incident is determined by comparing the energy values of the two digital signals.