To recover fluorescence returned from a sample not uselessly, even when using a low magnification and high numeral aperture of objective lens, and to obtain a fluorescence image of high resolution without lowering time-serial resolution.

This optical scanning confocal observation device 1 is provided with a light source 2, an optical scanning part 14 for scanning two-dimensionally excitation light from the light source 2, an objective optical system 5 for converging the scanned excitation light to irradiate the sample, a dichroic mirror 17 arranged between the objective optical system 5 and the optical scanning part 14 to separate the fluorescence from the return light from the sample A returned via the objective optical system 5, a convergence lens 18 for converging the separated fluorescence to form an intermediate image, a slit member 19 arranged in the vicinity of an intermediate image position, and arrayed alternately with a plurality of parallel slit-like fluorescence transmission part and shielding parts, a slit member moving mechanism 28 for moving the slit member 19 along an arrayed direction of the fluorescence transmission part and the shielding parts, and a photodetector 21 for detecting the fluorescence transmitted through the fluorescence transmission part of the slit member 19.