In a radiation image storage panel which has a phosphor layer containing energy-storing phosphor particles, the energy-storing phosphor particles is composed of a mixture of a phosphor particle group having a relatively large median diameter and a phosphor particle group having a relatively small median diameter, the former group having a median diameter of 4 to 30 μm, the latter group having a median diameter of 1 to 8 μm, and the mixture having a particle size frequency distribution that satisfies the condition of: (x+y)/5>z in which x is a size frequency (%) at the peak in a larger range of the size frequency distribution curve, y is a size frequency (%) at the peak in a smaller range, and z is the lowest size frequency (%) in the range between the two peaks.