To combine a scintillator array with photomultipliers to provide an inexpensive radiation detector reduced in the number of photomultipliers without lowering sensitivity and resolution.

The scintillator array 1 arranged two-dimensionally with scintillators is made partially luminescent by incidence of a γ ray, a light transmission part of a liquid crystal panel in a detection window 2 arranged in a backface thereof is scanned electrically in lines and rows by a detection window control unit 4, and emitted light is guided to one photomultiplier 3 provided in a following stage. An output signal of the photomultiplier 3 is transmitted to a measuring unit 5 via signal line 6. The measuring unit 5 specifies the scintillator incident with the γ ray and measures intensity thereof, based on a position signal from the detection window control unit 4 and an intensity signal from the photomultiplier 3.