Gerard Carayon, a longtime resident of the Javanese capital Yogyakarta, denies the charges.
Carayon headed a non-governmental organisation which helped children in distress and some of them worked at his house.
In 2004, a French diplomat in Jakarta alerted Indonesian police about suspicions that Carayon was sexually abusing children in his house or at a hotel.
A probe was launched and the boys told an Indonesian teacher they had been raped or abused and sometimes given money in exchange for sex.
Carayon, who described himself as a painter, denied the allegations in court. When the testimony of an alleged victim was read out in court that he served as a sex slave, Carayon murmured: “It’s not true.”
He was arrested at Paris’s Charles de Gaulle airport in 2008 while returning from Cambodia. He was released after 18 months in detention in March 2010 under a judicial review but disappeared, sparking an arrest warrant.
Carayon was then arrested in August near the Franco-Italian border and detained again.
Suspected child abuse offenders are being increasingly judged in their own countries for offences committed abroad following changes in legislation in nearly 40 countries.