PURPOSE: To simplify an electric contact structure, to improve reliability, and to reduce a cost and thickness by providing a movable contact pin, which, is brought into contact with both of a lens side contact and a camera contact and is supported movably in the optical axis direction.

CONSTITUTION: An extension tube 1 which is arranged between a camera body 10 and an exchangeable lens-barrel 30, is provided with a movable contact pin 2, which is provided with a cup part serving as a gap part in an approximately central part, a guide 3, which is fixed in an inside diameter of the extension tube and serves as an insulator for the movable contact pin 2, a contact pin guide cover 4, which is made of an insulator so as to prevent the movable contact pin 2 from being removed from the contact pin guide 3, and an extension tube 5. The movable contact pin 2 is supported by the contact pin guide 3 and the contact pin guide cover 4 so as to be slightly movable in the parallel direction to an optical axis A-A'. In this case, a spring 14a pressing a movable contact pin 14 inside the camera body 10 is used for a contact pressure generating spring for the movable contact pin 2 inside the extension tube 1.