In a lens-fitted film unit provided with an unexposed film having an ISO sensitivity Sviso; a lens having a fixed focal length of f (mm) and a fixed f-number F; a shutter having a fixed shutter speed T (sec); a system sensitivity index S is larger than 0 and not larger than 4.5; wherein the system sensitivity index S is represented as follows: S=EV value Ev-Film sensitivity index Sv, Ev=3.32 log.sub.10 (F.sup.2 /T) Sv=3.32 log.sub.10 (0.3.times.Sviso)