The 27-year-old is set to lead Team Sky at the event, with last year's yellow jersey winner Sir Bradley Wiggins focusing on the Giro d'Italia.
The British rider told reporters: "I don't believe he is completely unbeatable. If you look at last year's Vuelta, he was sitting in second or third place coming into the last week.
"I feel I can win the Tour. It is going to be a hard challenge, especially with the likes of Contador there, possibly [Joaquim] Rodriguez, Andy Schleck returning, Cadel [Evans], Tejay van Garderen. Tejay is only getting stronger every year.
"It is going to be hard work. I believe it is a harder ask than last year."
Froome finished second in the general classification at last year's Tour, but this year's mountainous route is expected to favour his riding style.
Contador has previously won the Tour de France twice, having been stripped of a third title for doping, and claimed the red jersey at the 2012 Vuelta a Espana shortly after returning from suspension.