Provided is a radiation generating apparatus, including: a radiation generating unit for emitting radiation; and a movable diaphragm unit including a light projecting/sighting system for making a simulation display of a radiation field with visible light. The light projecting/sighting system includes: a light source of the visible light; a light guiding plate that is provided across a radiation axis, and causes the visible light from the light source to exit from a front surface of the light guiding plate; and a louver that gives directivity to the visible light exiting from the front surface of the light guiding plate.