As of Thursday, no one had been charged in the insider trading inquiry, launched in November 2006 following legal action by shareholders in the aerospace group.
Both Eads and Airbus have declined to comment on Forgeard's detention.
Forgeard, who resigned in July 2006 over the claims, insists he was unaware of the depth of the A380 production difficulties when he sold large quantities of stock.
In an interview in October last year he said: "I am judged guilty, even though nothing has been proven. And nothing will be proven because there is nothing."
He said he was being made "a convenient scapegoat".
France's financial market regulator, the AMF, said in April it had found evidence of possible insider trading by Forgeard and 16 other Eads executives including Thomas Enders, a former Eads co-chief executive and current chief executive of Airbus.
It also suggested the group's principal shareholders, Lagardere, the French media and technology company and Daimler, a German car manufacturer, had sold stock on the basis of "privileged information" about the group's troubles.