To obtain a radiation-detecting device that has high sensitivity, high sharpness, high S/N ratio, and low electric noise, and is inexpensive.

The radiation-detecting device comprises a phosphor layer 7 for converting radiation to light, and a photodetector consisting of a plurality of photoelectric conversion elements 2 for converting light by the phosphor layer to an electric signal. In the radiation-detector, the phosphor layer 7 is composed of a first phosphor region 8 containing a large-particle-diameter phosphor particle and a small-particle-diameter phosphor particle, and a second phosphor region 9 containing a small-particle-diameter phosphor particle which are integrally arranged alternately in the direction of vertical to the surface of the photodetector.