PURPOSE: To enable detection of fine foreign particles to satisfy both a resolving power and sensitivity.

CONSTITUTION: A radiation detector 6 has almost an uniform thickness in a range of 50-1,000μm and a light shielding partition 2 is provided across the width thereof with a width thereof below 50μm and a pitch thereof below 200μm. It is made up of a scintillator section 1 having a light reflection layer 16 formed on a radiation irradiating surface, a light waveguide 3 which allows transmission maintaining an emission distribution with the scintillator section 1 in substance and a photoelectric convertor section 4 which has a partition 5 for optical division across the width and receives light from the light waveguide 3 to be converted into electricity. The light shielding partition 2 of the scintillator section 1 is arranged corresponding to the partition 5 for optical division of the photoelectric convertor section 4.