A radiation image detector comprising: a scintillator panel comprising a radiation transmitting substrate having thereon a phosphor layer having a columnar crystal structure produced with a vapor deposition method a protection cover provided at a side of the radiation transmitting substrate opposite the phosphor layer, provided that incident radiation enters through the protection cover and a flat light-receiving element provided at a side of the radiation transmitting substrate opposite the protection cover, the flat light-receiving element comprising a plurality of light-receiving pixels arranged in a two-dimensional form and capable of converting light emitted from the scintillator panel to electricity, wherein the radiation image detector satisfies the following Formula (1): W(g)<0.31(g/cm2)xS(cm2)
