Planet of the Apes or La Planète Des Singes or Monkey Planet. Whatever. Translated into English by Xan Fielding.
Okay, now, you have to remember that the original novel and the movie deviate in certain major ways. The end twist is completely different, for example, and the main character is a journalist who is essentially just along for the ride, not an American astronaut. He's also a lot less... Hestonish, if you will, of course. More intellectual, less "get your stinking paws off me." I love the movie, by the way, and consider it a classic, but had to sort of ignore it in reading the novel.
You can read this one as a straight ahead 60s scifi story, and a damn good read it is. From the curiosity of the travelers as they first encounter the inhuman humans to the panicked frenzy of Mérou escaping death at the hands of gorilla hunters to the strange love triangle of intelligent human/primitive human/intelligent chimpanzee, there's no mystery as to why the basic concept could be so well translated to the screen.
If you are inclined that way, as I sometimes tend to be, you can also read it as paranoia about "lesser" races rising up to surpass and suppress European culture. With all the devolved people being depicted as beautiful and white - and the common racist portrayal of Africans as apes - this isn't exactly a stretch. But then, I may be playing Boulle false to assume that comparison was intended. I haven't studied him enough to know one way or the other.
The little details, mostly of ape culture, were what I enjoyed most about this one. Their stock market, with various apes flinging themselves around a giant room, climbing into the rafters, all shrieking at the tops of their lungs as they buy and sell, is a memorable image. The idea that the chimp scientists focus so strongly on biological and brain studies because that's the last thing their unevolved ancestors were used for by human was inspired. And, of course, Zira's refusal of the human Mérou because he's "just so ugly" - a great moment.
final thought: Our nearest cousins, and the ones most likely to overrun us in the end. Who doesn't feel that apes are just slightly too human sometimes?