It has been the law since July 1, 2008
So woe betide any driver stopped by the police and discovered not to have one somewhere in the vehicle.
A €90 fine can, and in all probability will, be issued, with the letter arriving in the post a couple of days.
And that's what one motorist from the town of Capbreton in the southwest of France expected after he returned from holiday, knowing that he had been stopped and found to be driving at the end of September without the required warning triangle shortly before leaving.
A letterbox stuffed full of fines (screenshot TF1 news report)
Except Gilles Rocher got more than he bargained for when he opened his letter box because he had been sent not just one, but 143 fines for the very same infraction - amounting to the princely sum of €12,870.
"I had fully expected a fine as I had been told I would be sent one," he told TF1 news.
"But surprise! Instead of just the one, I received 143 each with a different number meaning that I had apparently broken the law not just once but 143 times."
Worse still, he somehow had to find the money to pay the fine - or should that be fines - within 15 days or risk a penalty charge being levied.
When he rang the hotline of Le Centre Automatisé de Constatation des Infractions (CACIR) to find out what he should do, his story was met with a certain incredulity and the best advice he was offered was to contest each of the fines individually in writing - and by recorded delivery.
143 fines for one infraction (screenshot TF1 news report)
Fat lot of help that was.
But thankfully the camera crews were around and journalists were on to the story.
A call to the interior ministry brought a response from one of its spokesmen, Pierre-Henry Brandet.
"If it becomes apparent that there has been a bug in the system, as seems to be the case, then the tickets will be immediately cancelled and there'll be no need to pay," he said.
"It's a regrettable incident but one which remains anecdotal."
Not for poor Gilles perhaps, who must have had the shock of his life
But the following day, as the regional daily, Sud Ouest reported, everything had been resolved.
All 143 fines had been annulled - including the original one.