His comments have upset public-sector teachers' unions and parents' groups, which have accused him of reviving the "schools war" between secular state and private Catholic education.
Interviewed on a Catholic radio station, he said private education was also national education, which provided freedom of choice, and that is was necessary to "give equal resources to public and private education so this choice can be exercised".
Observers were surprised last week when Mr de Robien made an official visit to a private Catholic school, an unprecedented move by an education minister, who is head of the strictly secular state system.
More than 2 million pupils attend private Catholic schools, compared with about 10 million in the state sector.
The private schools are under contract with the government, which pays teachers' salaries. They teach the national curriculum and are inspected by state inspectors.
Religious education is not compulsory and annual fees vary between l150 (Pounds 100) in primary schools and l1,200 at a typical Parisian secondary school.
Mr de Robien was apparently using the radio interview as an opportunity to respond to the frustrations of the private sector, which has become a victim of its own success. Since 2002, an extra 23,000 pupils have enrolled, but thousands have been turned away because of a lack of places.
At the same time, the number of teachers has fallen.
The government decides on the number of teaching posts, which is indexed to the number in the public sector. This year, there are 532 fewer teachers in private schools, despite 3,200 extra pupils. Some classes have more than 40 pupils.
After Mr de Robien's broadcast, the parents' association FCPE and the main teachers' federation of unions, the FSU, said the minister was reviving the state-church "schools war" that waged during the 19th century.
Relations between the two sectors continue to be uneasy. Unions said the minister's comments were "stupefying" and "provocative" and feared that Mr de Robien wanted to "give extra resources to private schools".
But an education ministry representative said that there were no plans to change the way private education is funded.
The minister's remarks provide another grievance for public-sector teachers, who are already planning a strike on October 4 in protest against education reforms and another austerity budget.