The present invention provides a method of preventing or reducing X-ray-induced temporal changes of a semiconductor photoelectric conversion film formed on a TFT substrate, in which a protective film or sheet is used to protect the semiconductor photoelectric conversion film in order to improve weather resistance such as light blocking effect and moisture resistance. The present invention provides a radiation detecting element characterized by including a substrate having a plurality of pixel areas formed thereon, each having at least one switching element and at least one charge storage capacity, a photoelectric conversion film formed on the individual pixel areas for converting radiation into electrical charge, a protective film individually covering the photoelectric conversion film and having an area that is substantially the same as or larger than that of at least the photoelectric conversion film and a seal member and a sealant arranged so as to enclose the photoelectric conversion film, for fixing the protective film.