PURPOSE: To reduce the size of an inspection apparatus by projecting a radiation energy beam through a window, correlating the energies reflected on the inner surface of the window and a tubular member and then determining damage on the inner surface of the tubular member thereby reducing power demand of the apparatus.

CONSTITUTION: A body 1 of circular cross section has a window 2 extending over the entire circumference of 360°. The optical path of an energy beam projected from a laser 14 extends through a fixed reflector 13 and a presenter reflector 10 to a rotary reflector 9 turning at high speed through a motor 7. The reflector 9 reflects the beam outward from the center to describe a circle on the window 2 thence describe a circle on the inner circumferential surface of a tubular member under inspection. Reflected energy from the inner surface of the window 2 and the tubular member is viewed by a radial reflector 8 and reflected toward a lens in a CCD camera 12. The reflector 8 excites the pixels in an array of the camera 12 depending on the intensity of light and the excitation of pixel is transmitted through a circuit 16 to a computer. Dimensional relationship between the axis of the body 1 and the window 2 are known, and a damaged state can be detected from these dimensions.