To provide an instant film pack, a method of assembling the same, and a holding tool for assembling the same, which enable sure junction between a main body case and a cover even in the case where a paper resin is selected as a material.

The instant film pack has a light shielding cover 13, a plurality of film units 14, and a light shielding sheet 15 stored in a case constituted of a case main body 11 and a cover 12. Even when what is called a paper resin having a constitution ratio of paper and thermoplastic resin is 51:49 to 75:25 is selected as the material, the main body case and the cover can be surely joined by snap fit fixation between an engaging hole 28 provided in the case main body 11 and an engaging projection 23 on a positioning projection part 24 provided on the cover 12.