A sample observation device includes a flow cell in which a fluid containing samples flows, an irradiation unit configured to irradiate the samples flowing in the flow cell with planar light, an image formation unit having an observation axis inclined with respect to an irradiation surface for the planar light, and configured to form an image of observation light generated in the sample due to the irradiation with the planar light, a two-dimensional imaging element configured to capture a light image including at least a cross section of the fluid among light images according to the observation light formed by the image formation unit, and outputs image data, and an analysis unit configured to analyze a light intensity profile of the sample in a flow direction of the fluid on the basis of the image data.