The medieval martial arts enthusiast who slapped President Emmanuel Macron across the face told a court he was a right-wing sympathiser who had acted because the president represented all that was rotten with France, BFM TV reported.

Damien Tarel, 28, told the court in Valence that several days ahead of Macron's visit to the southeastern Drome region, he had thought about throwing an egg or a cream tart at the president, the news channel reported.

"I think that Macron represents very neatly the decay of our country," he told the court, according to BFM TV. "If I had challenged Macron to a duel at sunrise, I doubt he would have responded."

Macron later described the attack as an isolated incident and said violence and hate were a threat to democracy.

Tarel faced a charge of assault against a public official, an offence which carries a maximum sentence of three years in jail and a 45,000 euro fine.

He struck Macron on Tuesday after the president came over to greet a small crowd of onlookers after visiting a professional training college during a trip to take the country's pulse as it emerges from the pandemic and ahead of presidential elections in 2022.

After Macron reached out to Tarel who was standing behind a security barrier, Tarel shouted "Down with Macronia" ("A Bas La Macronie") and slapped Macron on the left side of his face.

He could also be heard shouting "Montjoie Saint Denis", the army's battle cry when France was still a monarchy.

"It's a patriot's slogan," he was quoted as telling the court.

The unemployed 28-year-old told police investigators that he had been close to the anti-government "yellow vest" protest movement which shook the Macron presidency, and held ultra right-wing political beliefs.

Acquaintances of Tarel described a man who loved period role play and was not a troublemaker. The prosecutor said he was not a member of any political or militant group.

Tarel was arrested along with a second man from his hometown of Saint-Vallier.

Police found weapons, a copy of Adolf Hitler's autobiographical manifesto Mein Kampf, and a red flag with a golden sickle and mortar that is the international symbol of the communist movement in the second man's home, local prosecutor Alex Perrin said.

The second man will not face any charges related to the slapping but will be prosecuted for illegal possession of arms in 2022.