An observation device captures images at focal positions inside a sample container with an optical system that includes an objective lens; an objective lens actuator; an irradiation unit; a reflection light intensity detector; a focus controller that positions the focal point of the objective lens on a reflection surface imparting a peak in the reflected light intensity; and a counting unit. The focus control unit drives the objective lens actuator and positions the focal point on a reflection surface when a peak is detected in the reflected light intensity; and the counting unit counts the reflection surface when the focus control unit has positioned the focal point on the reflection surface. The computation unit determines whether or not the focal point is positioned at the focal position, and causes the optical system to capture images if the focal point is positioned at the focal position.