To allow a film unit with lens to additionally extend the focal length by mounting an adapter to the film unit with lens of a telephoto type already supplied in the market.

A teleconverter lens 26 is built in the lens barrel 26 of an adapter body 21. A positioning surface disposed on the rear end side within the lens barrel 26 is made to abut on the lens barrel front end 14 of the film unit with the lens of the telephoto type. A strap 24 fixed to the top plate of the adapter body 21 is turned around to the back side of the film unit with the lens and is hooked to a hook 25 disposed at the lower plat, by which the adapter body is mounted at the film unit with the lens. A visual field limiting frame 23 is positioned at the front of a finder objective window 15, thereby, the user carries out framing through the finder in an ordinary manner.