An observation device comprising: an imaging optical system that includes an imaging lens for forming an image of an observation target in a container accommodating the observation target; an operating section (15-15H) configured to perform at least one of a first operation of changing a focal length of the imaging optical system , a second operation of moving the imaging lens in an optical axis direction of the imaging lens , or a fourth operation of moving the container in the optical axis direction; a detection section that includes at least one displacement sensor (18a-18d) detecting a vertical position of the container ; an operation controller configured to control the operating section (15-15H) based on the vertical position of the container detected by the detection section ; a horizontal driving section configured to move at least one of the container or the imaging optical system in a horizontal plane orthogonal to the optical axis; and a scanning controller configured to scan the container by controlling the horizontal driving section to move an observation region (R) of the imaging optical system , wherein the detection section is configured to detect the vertical position of the container at a forward position of the observation region (R) in a horizontal movement direction with reference to a position of the observation region (R) of the imaging optical system with respect to the container and change a position of the displacement sensor (18a-18d) or the displacement sensor to be used (18a-18d) in accordance with a change of the movement direction of the observation region (R). an imaging optical system that includes an imaging lens for forming an image of an observation target in a container accommodating the observation target; an operating section (15-15H) configured to perform at least one of a first operation of changing a focal length of the imaging optical system , a second operation of moving the imaging lens in an optical axis direction of the imaging lens , or a fourth operation of moving the container in the optical axis direction; a detection section that includes at least one displacement sensor (18a-18d) detecting a vertical position of the container ; an operation controller configured to control the operating section (15-15H) based on the vertical position of the container detected by the detection section ; a horizontal driving section configured to move at least one of the container or the imaging optical system in a horizontal plane orthogonal to the optical axis; and a scanning controller configured to scan the container by controlling the horizontal driving section to move an observation region (R) of the imaging optical system , wherein the detection section is configured to detect the vertical position of the container at a forward position of the observation region (R) in a horizontal movement direction with reference to a position of the observation region (R) of the imaging optical system with respect to the container and change a position of the displacement sensor (18a-18d) or the displacement sensor to be used (18a-18d) in accordance with a change of the movement direction of the observation region (R). <EOS>