Eight-year-old Océane went missing on Saturday evening after going to visit a friend. Her body was found in a vineyard on Sunday morning after an extensive search involving police and 300 volunteers.
The autopsy revealed the girl had been sexually molested before being suffocated. She had also been stabbed four times, most likely after her death.
News channel LCI reported that the new suspect is a drug user who is known to police.
Public prosecutor Robert Gelli said the man "couldn't remember what he did on Saturday evening" as he was drunk. "He had a blackout" he said.
He is being tested for a DNA match and was still being questioned on Wednesday morning.
Earlier, a 73-year-old man who had been held for questioning since Sunday was released after DNA tests revealed no match. The man, a neighbour of the girl's family, had a previous conviction for sexual assaults on young boys.
Locals told journalists the uncertainty was causing continuing concern in the village of 6,000 inhabitants.
"We are looking at everyone, wondering who it can be. It must be someone from the village," said one woman, named Véronique, to news channel BFM TV.
Océane's parents are believed to have left the village to stay with relatives. A march in memory of the girl will be held on Wednesday.