A lens-fitted photo film unit contains a roll of photo film whose base layer is formed from annealed polyethylene naphthalate. The A-PEN base photo film has the same stiffness at a smaller thickness compared with the conventional TAC base photo film. The roll of photo film of the smaller thickness may have a smaller external diameter in a film roll chamber of the film unit than the conventional photo film having the same number of available exposure frames. Accordingly, the internal diameter of the film roll chamber and thus the thickness and the width of the unit body can be minimized.