By Agence France-Presse
"I won't go to Riyadh next week," Le Maire told France's Public Senat TV channel, adding that "the current circumstances do not allow me to go to Riyadh".
The minister echoed President Emmanuel Macron's remarks last week on Khashoggi's disappearance, calling it a "very serious" matter.
Le Maire is one of the first senior Western officials to pull out of the October 23-25 Future Investment Initiative in Riyadh.
US Treasury Secretary Steven Mnuchin has said he will decide on Thursday whether to attend.
Several business titans and Western media groups have already pulled out of the conference organized by Saudi Arabia's sovereign wealth fund.
Khashoggi, who was living in self-imposed exile in the United States where he contributed to the Washington Post, vanished after entering the Saudi consulate in Istanbul on October 2. He was critical of some of Saudi Arabia's policies.
Turkish officials claim he was killed and dismembered in the consulate by a hit squad which arrived from Riyadh -- claims denied by the Saudi government.