PURPOSE: To detect the structure defect of a metal by observing a metal sample through a microscope, picking up its image by a TV camera coupled with the microscope, and analyzing a characteristic value.

CONSTITUTION: An automatic focusing device which uses air flow flux and an automatic focus controller 6 controls a focus position by a DC motor as the sample moves. Further, a stage controller 7 drives and controls the stage of the optical microscope 2 in an X-axial and a Y-axial direction by a pulse motor under the command of a personal computer 4. Then an image obtained by the microscope 2 is inputted to the associated TV camera 3 and sent to an image analyzing device 1. The image analyzing device 1 where necessary programs and information are stored selects only a necessary image among many images having information and its data is sent to the personal computer 4 and processed. The analytic processing result is printed and recorded on the printer 5. Consequently, the defect of the metal structure is accurately detected without any operator's intervention.