"We kept them under pressure and there was quality in everything we did," coach Didier Deschamps said.
Ribery opened the scoring from the penalty spot after seven minutes and played a part in all the goals.
Giroud doubled the lead in the 16th minute with a superb curling shot over goalkeeper Mitch Langerak and the in-form Arsenal striker added a third goal 11 minutes later following good work by Ribery and Samir Nasri.
Ribery and Nasri were also involved in the fourth goal which came courtesy of a 20-metre drive from Yohan Cabaye.
Mathieu Debuchy made it 5-0 two minutes after the break and Benzema, booed when he came on as a substitute at half-time, completed the scoring from close range in the 50th minute.
The crowd chanted 'He has scored, he has scored' and Benzema responded by applauding the fans.
"I'm happy for him and for the team. He really needed that goal," said Deschamps.
Australia, hammered 6-0 by 2014 World Cup hosts Brazil last month, have now conceded 19 goals in four games.
"The result speaks for itself, we never really got into the game. France are a quality team and we could never really compete against them," said coach Holger Osieck.
France, second in Group I behind Spain, play their final World Cup qualifier at home to Finland on Tuesday.