A radiation imaging system comprises a radiation source and a radiation image detection device. The radiation image detection device has a solid state detector and a wavelength converting layer arranged in this order from a radiation-incident side. The wavelength converting layer detects radiation passed through the solid state detector and converts the radiation into visible light. The solid state detector detects the visible light and produces image data. The wavelength converting layer is a phosphor layer, being a single layer, in which at least first phosphor particles having a first average particle diameter and second phosphor particles having a second average particle diameter are dispersed in a binder. The second average particle diameter is smaller than the first average particle diameter. The weight of the first phosphor particles per unit thickness of the wavelength converting layer decreases with increasing distance from the solid state detector.