The incident was caught on tape. Sarkozy is seen shaking hands when suddenly, an arm reaches out and grabs Sarkozy by the lapel, nearly knocking him down in the town of Brax.
Sarkozy regained his balance, and his security detail immediately pulled the man to the ground.
The man did not have a weapon. He was detained and was being questioned in the nearby town of Agen.
Sarkozy was unhurt. His office is not commenting on the incident.
The outspoken and divisive president has had low poll ratings and has been heckled on occasion. He is expected to run for re-election next year.
The Associated Press contributed to this report.