Should I wait for my professor to reply my request for recommendation letter? I am going to apply to graduate programs in the US, so I contacted my professor who advised my master's thesis. He is the most important referee because I did research with him, so I think he understands me well. Moreover, he is a well-known scientist in a very prestigious university in France (top 20 of the world in my field). 

At the time, I left France to my home country, he told me that he would help me further my academic career. He actually gave me two recommendation letters afterwards for 2 PhD positions. Sadly, I failed both of them.

Ten days ago, I emailed him if he could give me recommendation letters. He didn't reply for one week, so I wrote a follow-up email. However, I haven't got any responses from him until now. I am so confused because the deadline is December 15th.

Does it mean that my professor has declined my request? Should I wait for him or ask other professors?

NEWS: I just got his acceptance. He was traveling this week so he didn't got my email. Thank you all for your advices.
Professors are really (really) busy. Most likely he simply did not have time yet to reply to your email. Or maybe he is at a conference and does not have access to the previous two letters on his office computer. He will probably reply to your message later.

To get his recommendation letter quickly the best thing you can do is make it as easy for him as possible. Because you already have two of his letters I suggest you write your own new recommendation letter based on these two, send it to him by email, and ask him to sign it. This is quite common, at least in the different labs in the UK and France where I have worked: many professors ask students to write their own letter, after which they may make a few changes and sign it. This saves them lots of time.

Also, make sure to let him know when your deadline is so he understands the urgency.