PURPOSE: To distinguish easily light irradiation field by providing a lens to condense the flux linear between the irradiation field diaphragm blade and light source of light boresight device and rotating the lens aroun the optical axis of the light boresight device.

CONSTITUTION: A cylindrical or semi-cylindrical lens to condense the flux of light linear between the irradiation field diaphragm blade and flood light boresight device which are contained in a x-ray movable diaphragm device in which the entire x-ray irradiation field is irradiated with a flood light boresight device. The light from the flood light boresight device is condensed to a linear flux passing the center of the light irradiation field lighting partially, and the cylindrical lens is rotated around the optical axis of the flood light boresight device. Accordingly the bright linear light from the flood light boresight device rotates in the light irradiation field, and the entire area of the light irradiation field can be distinguish easily without increasing capacity of the light source of the flood light boresight device.