PURPOSE: To satisfactorily visualize an observation object with an ultraviolet light by a simple constitution, by forming the observation object using a fluorescent substance which converts an incident ultraviolet laser light to a visible light.

CONSTITUTION: An ultraviolet laser 12 is radiated to a substrate 18 by a laser light source 10, and when a laser point is formed on the substrate 18, a fluorescence 22 is radiated from a fluorescent substance which has been provided on the substrate 18. The fluorescence 22 which has been emitted from this substrate 18 transmits through an objective lens 16, and a dichroic mirror 14, and on the other hand, reflected by a half mirror 24, and made incident on a photoelectric detector 30 through a lens 26. In this case, a switching mirror 28 is withdrawn from in an optical path as shown by a broken line, and the fluorescence, on the other hand, is reflected by a mirror 34 through a lens 32. In this way, by a photoelectrically converted signal from the detector 30 and a fluorescent image on an image pickup surface 36, a position of a laser spot can be measured satisfactorily without observing directly a laser spot.