A culture-vessel adaptor that is detachably fixed to the exterior of a culture vessel capable of holding a culture medium containing a specimen is provided. The culture-vessel adaptor includes a vessel mounting part where the culture vessel is mounted; and a protruding part disposed so as to extend outward from a side surface of the culture vessel when the culture vessel in mounted in the vessel mounting part. Handling of culture vessels becomes easy by an automated mechanism such as a robot, with a straightforward and low-cost method, and the culture vessels can be reliably prevented from being dropped.