PURPOSE: To form a radiation detecting system having a high position resolution by making many light emitting bodies (scintillators) correspond to one light receiving body (photomultiplier tube).

CONSTITUTION: A light emitting assembly 1 is constituted of three pieces of rectangular parallelopiped-shaped scintillators 1AW1C, and reflecting filters 3AW3C having each different reflection characteristic are placed on radiation incident surfaces of the scintillators 1AW1C, respectively. Also, a reflecting material is applied to all surfaces except the incident surface of the scintillator, and the emitting surface opposed to said surface, so that an emitted light beam by an incidence of γ rays does not invade an adjacent scintillator but led to a photomultiplier tube 10. On the inside surface of an incident window of a container of the photomultiplier tube 10, a photoelectric surface 11 is formed. A light beam which has been generated in the inside of the scintillators 1AW1C and has been influenced by the filters 3AW3C having each different reflection factor is made incident on the photoelectric surface 11 and a photoelectron is generated. This photoelectron is multiplied by dynode groups 12, 13, fetched through an anode 14, and an output pin 15, and which light emitting body has been excited from an output of a light receiving body 10 is decided by a deciding circuit 100, by which a radiation detecting system having a high position resolution is formed.