I can't tell you the maker, but it looks nice: that's a Gargette Bros BB shell (used by many builders in many countries) and what seem to be Prugnat lugs, but may be a similar pattern from another lug shop. BB threading and seatpost size will help determine if it's French or not, the tubing decal may be true or just put on cause it looked good.
Edit: upon re-reading, the fact it has Vitus dropouts and forkends really makes the case for it being Vitus tubing, and with the BB shell it is a strong argument for it being French...but threading and seatpost size will tell more. I still don't recognize the make based on other details.