According to The Sun, police wrestled the 25-year-old to the ground as he tried to break into the Elysee Palace, the French President's official residence. Cops found the weapons inside his military-style jacket.
Sarkozy was inside at the time, meeting Montenegro's Premier Milo Djukanovic.
His security guards are treating the lunchtime incident as an attempt on his life.
A witness said "There was a group of men at the main entrance when the guards suddenly pulled one man aside. There was a violent struggle before the man dressed in an army-type jacket was dragged down and held at gunpoint. He was pushed into a police van and driven off."
An official said on Monday that the man was in custody and being quizzed on suspicion of a plot to assassinate Sarkozy.