In a radiation detector in which scintillator layers are directly formed on all the light receiving parts of a plurality of photoelectric conversion substrates, space and level difference between the adjacent photoelectric conversion substrates are determined so that the effects of these space and level difference fall within a range corresponding to the effect of one photoelectric conversion element. Specifically, the space between the adjacent photoelectric conversion substrates is equal to or less than 133 μm and the level difference between the adjacent photoelectric conversion substrates is equal to or less than 100 μm. Accordingly, the scintillator layers can be directly formed on all the light receiving parts of the plurality of photoelectric conversion substrates. This prevents degradation in MTF and sensitivity and reduces manufacturing costs.