To more reliably fasten film units in a film pack body without damaging the film pack body.

A plurality of film units 14 and a light shielding sheet 16 are fastened in a stacked state to a film pressing plate 24 of a film pack body constituting an instant photo film pack by caulking a staple 22. At this time, a caulking height H of the staple 22 is adjusted to a range of 80±5[%] of [T1+T2+T3×2] from relation with the thickness T1 of a support portion 42 of the film pressing plate 24, the thickness T2 of the film units 14 and the light shielding sheet 16 in the stacked state, and the thickness T3 of the staple 22.