An ultrasound observation device includes a processor including hardware, wherein the processor is configured to: generate ultrasound image data； set, in a region of interest, a plurality of small regions by dividing the region of interest in accordance with a preset condition； generate a histogram of each of the small regions； calculate a determination value for each of the small regions； determine whether the physical quantity in each of the small regions is uniform； change a determination target small region in accordance with a preset condition when the physical quantity in the determination target small region among the small regions is determined to be not uniform； set the determination target small region as an attenuation rate calculation target region when the physical quantity in the determination target small region is determined to be uniform； and set an attenuation rate of the attenuation rate calculation target region.
