An intermediate member is disposed between a peripheral region and a third region, having been fixed to an imaging plate and a retaining plate. The intermediate member does not extend to between at least a part of a middle region and a forth region, such that a void is provided. The difference between the linear expansion coefficient of the imaging plate and the linear expansion coefficient of the intermediate member is smaller than the difference between the linear expansion coefficient of the retaining plate and the linear expansion coefficient of the intermediate member.