Hollande is on a three-day visit to Japan, the first by a French president in 17 years.
Speaking in French, Hollande expressed "the condolences of the French people to the Chinese people," referring to the Algerian hostage crisis in which ten Japanese people were killed in January.
He reportedly did not correct the mistake, though an interpreter did correct him in her simultaneous translation.
But journalists picked up on the error, and the insult -- to both sides -- spread on the internet. Neither side likes to be confused for the other, and there is mutual distrust between China and Japan.
French officials said President Hollande was tired.