A lens-fitted photographic film unit has a picture frame size changing mechanism for changing the size of picture frames between a full size and a panoramic size. The picture frame size changing mechanism includes upper and lower exposure aperture masking plates which are pivotally mounted in a light-shielding box in front of an exposure aperture. The masking plates are interconnected to each other through one-side contact and urged by a tension spring toward a full size position. The upper masking plate is connected to an operation knob through a crank lever and a switching lever. When the knob is operated to select the panoramic size, the switching lever is moved over a necessary amount for moving the masking plates in a panoramic size position to mask the exposure aperture. After the masking plates are stopped in the panoramic size position by stoppers, the over-stroke of the switching lever is absorbed by resilient bending of the crank lever.