A clear fluorescence image is easily obtained irrespective of variation of scattering due to variation of the depth of a focus position in a specimen. A scanning optical device includes a laser light source for emitting laser light, a scanning unit for scanning the laser light emitted from the laser light source on the specimen, a focus depth adjusting unit for adjusting the depth of the focus position in the specimen of the laser light to be scanned, a fluorescence detector for detecting fluorescence generated from the focus position of the laser light in the specimen, a reference depth information storage unit for storing the absolute height of a predetermined reference depth of the focus position of the laser light in the specimen by the focus depth adjusting unit, and a hardware setting storage unit for storing the relative height to the absolute height of the reference depth at each focus position of the laser light and at least one set value of the laser light source, the scanning unit, and the fluorescence detector in association with each other.