An imaging condition set in a first region of a three-dimensional model of a subject and an imaging condition set in a second region of the three-dimensional model are different from each other. A processor of an observation device determines whether or not the imaging condition that has been set in the first region or the second region including a position on the three-dimensional model is satisfied. The position is identified on the basis of a position of an imaging device and a posture of the imaging device. The processor displays observation information on a display on the basis of a result of determination. The observation information represents whether or not the first region or the second region including the position on the three-dimensional model has been observed.