To accurately and multiply detect the generation of abnormality in a measuring object.

This method is provided with an irradiation process (step S1) for irradiating respective points of a measuring object with plural laser beams oscillated by a laser beam resonator, a light receiving process (step S2) for receiving respectively the beams returned from the respective measuring points of the measuring object, which are the laser beams emitted from the irradiation process S1, and a photoelectric conversion process (S3) for converting photoelectrically respectively the laser beams received in the process S2 and self-mixed with laser beams oscillated in the resonator. A vibration quality determining process (S4) is provided also to determine the quality of vibration of the measuring object based on conditions of beat waves in the respective points of the object converted in the process S3 to be output.