PURPOSE: To easily perform the analysis of data and to judge a case when the strength of a light spot exceeds a rated value accidentally as abnormality by accumulating a measuring value by providing a storage part, and inspecting the normalcy or the abnormality of an output signal from a two-dimensional light position detector.

CONSTITUTION: The storage part 4 stores A/D data (g). A control part 5 generates a select signal (e) and a timing signal (f) based on a measuring condition inputted by a keyboard 6. Furthermore, inspection is performed by comparing the A/D data (g) stored in the storage part 4 with a reference value obtained by the light spot made incident on with normal strength. When it is judged that the abnormality occurs, an error is outputted to a display output part 7, and when it is normal, an X position signal and a Y position signal are calculated from a measured result based on an output format inputted by the keyboard 6, and outputted to the display output part 7. In such a manner, it is possible to easily perform the accumulation and analysis of the data, and also, to judge the case when the strength of the light spot exceeds the rated value accidentally as the abnormality.