The ex-general is being held on suspicion of divulging information on the multi-million-dollar KF-X stealth fighter development programme, an official at the prosecutors’ office in Seoul told the AFP news agency on condition of anonymity.
He declined to give details.
Yonhap news agency said the man, identified only as Kim, allegedly took classified photographs from a special library at the Korea National Defence University.
Based on the images, he later wrote documents in English and delivered them to Saab officials between August 2008 and May this year, it said.
The agency said Kim, who was once involved in the fighter project and now runs a consulting company, sought access to the library’s confidential reports for research purposes, citing his enrollment in a university graduate course.
The defence ministry said last week that security authorities were probing Saab’s local branch amid allegations it paid a local research firm called the Security Management Institute to secure classified information.
Saab has been interested in the fighter project, Yonhap said last week, adding its potential competitors include US firms Boeing and Lockheed Martin.
Investigators suspect the institute has presented reports on the fighter project to parliament in favour of Saab, it said.
Saab, according to the UK Financial Times, has acknowledged that its South Korean premises had been inspected but denied any wrongdoing and said it was co-operating with the investigation.