Patent attributes
Before an observation region of an imaging optical system (14) reaches an observation position in the cultivation container (50), a vertical position of the cultivation container (50) at the observation position is precedently detected by an auto-focus displacement sensor. In a case where an objective lens is moved in an optical axis direction on the basis of the position, an error between the precedently detected vertical position of the stage (51) at the observation position and a vertical position of the stage (51) at a time point when the observation region of the imaging optical system (14) is scanned up to the observation position is acquired, and the objective lens is moved in the optical axis direction on the basis of the error.