A radiation image capturing system includes a radiation source and a radiation image detecting device. The radiation image detecting device includes a solid-state detector and a wavelength conversion layer disposed in this order from a radiation incident side. The wavelength conversion layer has a first phosphor layer having first phosphor particles dispersed in a binder, and a second phosphor layer having second phosphor particles dispersed in a binder. The average particle diameter of the second phosphor particles is smaller than that of the first phosphor particles. The first phosphor layer is disposed on the side of the solid-state detector relative to the second phosphor layer, and joined to or pressed against the solid-state detector. The first and second phosphor particles are distributed in the first and second phosphor layers, respectively, such that the weight of the binder per unit thickness is gradually decreased to the side of the solid-state detector.