There is provided an optical analysis technique using the optical system of a confocal microscope or a multiphoton microscope for optical analysis techniques, such as the scanning molecule counting method, FCS, FIDA and PCH, in which it is enabled to judge whether or not a predetermined condition in the optical system is realized before performing a light intensity measurement. In the inventive optical analysis technique of measuring light intensity from a light detection region placed in a sample solution and analyzing the light intensity, there is performed a process of judging if a light detection region is placed in the sample solution and a measurement of the light intensity from the light detection region can be performed, and/or, the position or its area of the light detection region relative to the sample container in which a light intensity measurement can be performed based on the magnitude of signal intensity outputted by a photodetector during moving the position of the light detection region rela
