PROBLEM TO BE SOLVED: To provide a radiation detection device and a CT apparatus capable of improving detection efficiency of fluorescent light emitted from a fluorescence substance.SOLUTION: The radiation detection device includes: a scintillator a light detection element array including plural cells each having a resistance, which are disposed along a part of the periphery of an active area of an avalanche photodiode for detecting visible light emitted from the scintillator and a reflection member for reflecting the visible light disposed in at least an area excluding the active area, an area excluding the resistance and an area excluding the outer periphery of the light detection element array, which are plane including the active area.
