A back-illuminated energy ray detecting element 1 includes a semiconductor substrate and a protective film. The semiconductor substrate has a first principal surface as an energy ray incident surface and a second principal surface opposite to the first principal surface, and a charge generating region configured to generate an electric charge according to incidence of an energy ray is disposed on the second principal surface side. The protective film is disposed on the second principal surface side of the semiconductor substrate to cover at least the charge generating region, and includes silicon nitride or silicon nitride oxide. The protective film has a stress alleviating section configured to alleviate stress generated in the protective film.