PURPOSE: To center a lens easily and accurately by bringing a contact piece which is slidable radially into contact with the tip of a piston which slides in an optical axis direction, and clamping the lens with the contact piece.

CONSTITUTION: A main body 13 and a box-shaped clamp 12 are coupled together by an elastic member 17, and the piston 15 is fitted in their center hole slidably in the optical-axis direction. The contact piece 15 is provided in the clamp 12 so that it is slidable radially through an elastic member 18, and the piston 16 and contact piece 15 contact each other. The lens 3 is clamped between a clamp pipe 1 and the contact piece 15, and when the piston 16 is slid to left, the contact piece 15 spreads along a lens spherical surface. In this case, the tip of the contact piece comes into dynamic contact, so its coefficient of friction is small and the lens 3 moves easily to perform the accurate centering easily.