A radiation detector for detecting irradiated radiation that includes: a converting layer for converting radiation irradiated from a radiation source capable of irradiating radiation from two imaging directions, which are different from each other, into electric charges; and a plurality of pixel electrodes for collecting the converted charges. In the radiation detector, when at least one of the two imaging directions forms a specified angle θ with respect to the direction that is orthogonal to the detector plane of the radiation detector, the thickness d of the converting layer and the sizes p of the pixel electrodes satisfy the condition: d·tan θ