The Baccalauréat, often known simply as the Bac, is taken by most French 18-year olds at the end of their time at secondary school.
The question in the maths exam, about probability, was circulated online and by phone before the exam was taken by 165,000 students last Tuesday.
According to Europe 1, the man is an employee of a company that repairs the printers that were used to print the exam papers. His 19-year old son had been questioned earlier in the day.
The man's wife told Europe 1 that she did not believe her husband was involved.
"He's been repairing machines that print confidential documents for 30 years. He never talks about it at home and the security controls are so strict that he never sees the documents."
Le Figaro reported a source close to the enquiry saying that the son of the man had given the exam paper to another boy who had taken a photo of it.
This photo eventually found its way on to a video game website on the 20th June, the day before the exam took place.
While the investigation continues Luc Chatel, the education minister, has decided to cancel the question concerned as the papers get marked. Instead, points will be used from the other three problems in the paper and the pass mark will be lowered from 10 to 9.
This decision has sparked outrage among many pupils and parents who have complained that the approach is unfair. Some are demanding that the exam should be taken again while others think the full four points for the question should be awarded to all. One parent has launched a legal challenge.
Bac season has been marked by a series of problems this year. Rumours have also circulated of similar leaks in the physics and English exams.
President Sarkozy yesterday gave his backing to his minister, saying that there was no "good solution" but the "most respectful" way of ensuring fairness had been chosen. Results from the Bac are due next week.