An optical-scanning observation device includes: a light source unit outputting illumination light； a light scanning unit scanning the illumination light； a light detection unit detecting signal light produced at each scan position and generating and outputting a light detection signal based on intensity of the signal light； a power supply unit supplying power to the light detection unit； a determination unit determining, every time the light detection signal is output, whether the intensity of the signal light is equal to or greater than a threshold set on the basis of a current capacity of the power supply unit； and an image generating unit generating an image having a pixel value based on the intensity of the signal light. The image generating unit generates an image having a saturated pixel value in a region determined that the intensity of the signal light is equal to or greater than the threshold.
