The present invention discloses a device for observing a flow state comprising a translucent duct. It further comprises an irradiation unit irradiating projection light, a condensing unit condensing the projection light along a length direction with respect to an axial core area of the translucent duct in which a fluid flows; and an image pickup unit for picking up images of scattered reflected light from an axial core area of the translucent duct at a plurality of times.
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