The poster depicts photos of François Hollande, Nicolas Sarkozy, Jacques Chirac and François Mitterrand with lipstick marks on their faces and the caption: "What do they all have in common?"
The billboard campaign by Ashley Madison, an online dating service for married people intent on infidelity, would have had little trouble coming up with a cast of characters, given recent reports on France's unfaithful political class.
A biography of France's first lady Valérie Trierweiler out this month claimed she was once in a ménage à trios with Mr Hollande and a Right-wing former minister. The prime minister carried out a prolonged affair with Miss Trierweiler before leaving his former partner and mother of his four children, Ségolène Royal, in 2007.
The late François Mitterrand spent many nights with his mistress, Anne Pingeot, with whom he had a secret love child, Mazarine. Her existence was only revealed at his death.
Jacques Chirac once admitted: "There have been women I have loved a lot, as discreetly as possible." His many alleged conquests include the Italian film actress Claudia Cardinale and were documented in a "drive-and-tell" book by his former chauffeur, Jean-Claude Laumond, published in 2001. In the 1980s, Mr Laumond says, the steady stream of women walking into Mr Chirac's office was so constant that female staff would joke: "Chirac? Three minutes. Shower included."
Mr Chirac insisted, however, that there had never been "any question" of him leaving his wife.
Hélène Antier, spokesman for the Ashley Madison's website, said it was prepared for legal action.
She said: "We believe we are free to use their images. And is there is any legal action, we will deal with it.
"But I hope that instead, this will make them laugh. It's poking fun, like a caricature. There is a culture of infidelity in France."
None of the three living leaders have reacted to the poster, but Mr Sarkozy has previously taken legal action.
Budget airline Ryanair was forced to pay out 50,000 pounds for a press advertisement before he married Carla Bruni in 2008 with a picture of the couple captioned: "With Ryanair, my whole family can come to my wedding."
The couple also sued clothes company Pardon for using a nude image of Madame Bruni on a bag, with the slogan: "My boyfriend should have bought me Pardon."
Ashley Madison - whose motto is "Life is short Have an affair" - has used billboards with political figures before, including pictures of Boris Johnson, the mayor of London, Silvio Berlusconi, the former Italian prime minister and King Juan Carlos of Spain.
Noel Biderman, founder of the eight-year-old site, which claims to have 16 million members, insists infidelity "will save marriage".
Shortly after the site's UK launch in 2010, he told the Daily Telegraph: "It can be a cathartic outlet which allows the person to become a better wife, husband, parent or boss. Just look at Bill and Hillary Clinton: sometimes being unfaithful can act as a litmus test to see whether it's worth persevering with a relationship.
