To provide a method for producing instant films, at a low cost, to which a conventional production line of instant films can be diverted and by which a positioning opening can be formed in conformity with each printed image of a mask sheet material.

Images for decoration which are different for every instant film and reference lines 35c are printed on a mask sheet material 15. The mask sheet material 15 is transported by a transport roller 52, and when one of the reference lines 35c is detected by an image sensor 50, the transport of the mask sheet material 15 is stopped. A positioning opening 49 is formed near a reference line 35c with a punching device 51 located on the downstream side. In the subsequent steps, the instant films are produced on the basis of the positioning openings 49 just like a conventional production line of the instant films. Since the reference lines 35c and the positioning openings 49 are located within the formation ranges of image plane openings 10 punched out from the mask sheet material 15, the designing performance of decorative printing is not lowered.