A microscope device comprising a stage, an objective lens, and a focus adjustment device, the focus adjustment device comprising: an interface detector arranged to detect a position of an interface present in a container containing an observation object, arranged on the stage of the microscope device; a controller; and an image capture unit; characterized in that: the controller is arranged to perform focus maintenance control for maintaining a focal position of the objective lens of the microscope device in a reference position distant from the interface detected by the interface detector in a direction of an optical axis of the objective lens by a predetermined distance when the image capture unit is not capturing images and while moving the stage in the direction perpendicular to the optical axis of the objective lens; and the controller and the image capture unit are arranged such that, in a time period when the image capture unit is capturing an image, the controller is arranged to change the focal position to a plurality of positions of the observation object from the reference position by moving at least one of the objective lens and the observation object in the direction of the optical axis, which causes the image capture unit to: capture an image at each position of the plurality of positions of the observation object to acquire a plurality of images; detect an optimum position for capturing an image of the observation object on the basis of the plurality of images acquired at the plurality of positions; and capture an image of the observation object at the optimum position for capturing an image. an interface detector arranged to detect a position of an interface present in a container containing an observation object, arranged on the stage of the microscope device; a controller; and an image capture unit; characterized in that: the controller is arranged to perform focus maintenance control for maintaining a focal position of the objective lens of the microscope device in a reference position distant from the interface detected by the interface detector in a direction of an optical axis of the objective lens by a predetermined distance when the image capture unit is not capturing images and while moving the stage in the direction perpendicular to the optical axis of the objective lens; and the controller and the image capture unit are arranged such that, in a time period when the image capture unit is capturing an image, the controller is arranged to change the focal position to a plurality of positions of the observation object from the reference position by moving at least one of the objective lens and the observation object in the direction of the optical axis, which causes the image capture unit to: capture an image at each position of the plurality of positions of the observation object to acquire a plurality of images; detect an optimum position for capturing an image of the observation object on the basis of the plurality of images acquired at the plurality of positions; and capture an image of the observation object at the optimum position for capturing an image. the controller is arranged to perform focus maintenance control for maintaining a focal position of the objective lens of the microscope device in a reference position distant from the interface detected by the interface detector in a direction of an optical axis of the objective lens by a predetermined distance when the image capture unit is not capturing images and while moving the stage in the direction perpendicular to the optical axis of the objective lens; and the controller and the image capture unit are arranged such that, in a time period when the image capture unit is capturing an image, the controller is arranged to change the focal position to a plurality of positions of the observation object from the reference position by moving at least one of the objective lens and the observation object in the direction of the optical axis, which causes the image capture unit to: capture an image at each position of the plurality of positions of the observation object to acquire a plurality of images; detect an optimum position for capturing an image of the observation object on the basis of the plurality of images acquired at the plurality of positions; and capture an image of the observation object at the optimum position for capturing an image. capture an image at each position of the plurality of positions of the observation object to acquire a plurality of images; detect an optimum position for capturing an image of the observation object on the basis of the plurality of images acquired at the plurality of positions; and capture an image of the observation object at the optimum position for capturing an image.