The present invention provides a solid scintillator comprising a rare earth oxide sintered body, wherein: an afterglow time, which is the time required for a light output from the solid scintillator to degrease from a maximum value to 1/e of the maximum value, is 200 ns or shorter. The rare earth oxide sintered body preferably has a composition represented by a general formula (1): LnaXbOc:Ce  (1), wherein Ln is one or more elements selected from Y, Gd and Lu; X is one or more elements selected from Si, Al and B; and a, b and c satisfy 1≦a≦5, 0.9≦b≦6, and 2.5≦≦c≦13, respectively.