Several pictures of Kim have been released since widespread rumours emerged in mid-August suggesting that he had suffered a stroke, however doubts have been cast over whether the images are current.
"The photos that have just been published seem recent and authentic to me. I can't say more because of medical confidentiality and state secrecy," Roux told Le Figaro.
"I have the impression that he is in charge in North Korea."
Roux also said that Kim's health was improving.
Le Figaro said that Roux travelled to Pyongyang, North Korea's capital, in October, but the doctor declined to provide any details of the visit, citing a doctor-patient confidentiality.
South Korean officials have said Kim underwent brain surgery after suffering a stroke in August, raising questions about the leadership of the communist nation as Kim has not publicly named a successor.
Analysts have said many local residents had heard about Kim's suspected illness, even though the government and media avoids any comment that would indicate its "Dear Leader" has been debilitated.