An adapter device, which is configured to couple an endoscope with a medical appliance, such that the medical appliance is provided to generate light to illuminate an object to be investigated by an endoscope, includes an adapter body with a through-hole through which light generated by the medical appliance can be transmitted, and a fastening device to removably secure the adapter body on the medical appliance. The side of the adapter body that is to face the medical appliance is configured to be held form-locked in a predetermined angle position when the adapter body is secured on the medical appliance.