A radiation detecting apparatus includes a sensor panel that has photoelectric conversion elements; a light source unit that has a light guide plate, a light-emitting source disposed at a side surface of the light guide plate, a diffusing plate disposed at one surface of the light guide plate, and a reflective plate disposed at an opposite surface of the light guide plate; and a support substrate that supports the light source unit. The light source unit is provided between the sensor panel and the support substrate. Multiple protrusions of the diffusing plate are in contact with a surface of the sensor panel. The light source unit is adhered to the sensor panel via an adhesive, and the adhesive extends to the support substrate.