The officer was a lieutenant-colonel stationed with NATO in Italy.
The French government is investigating a senior military officer over a “security breach”, the defence minister said on Sunday.
According to French media reports, the top officer is suspected of spying for Russia.
“What I can confirm is that a senior officer is facing legal proceedings for a security breach,” Defence Minister Florence Parly told French media, giving no further details.
France's Europe 1 radio reported that a French lieutenant-colonel based in Italy and stationed with NATO is believed to have transmitted sensitive documents to Russia's secret services.
The man was arrested by the French intelligence agency DGSI as he was preparing to leave for Italy at the end of his holidays in France.
He is being held at a prison in Paris, Europe 1 said.
