PURPOSE: To enable common use for observation and treatment of parts inside an eye ball and better adaptation to the position of treatment depending on a patient regardless of a slight difference.

CONSTITUTION: In a contact lens 50 for intraocular observation which has a lens body 70 with a concave surface 72 made to contact the surface of a cornea of an eye to be inspected and has an incident lens 76 which is made to contact a plane 74 of the lens body and movable on the plane, a positioning mechanism (a groove 62 and slide part 80) is provided between the lens body and the incident lens thereby enabling the incident lens to be positioned at a plurality of positions on the lens body.