The professor takes me only if I continue up to finishing PhD. What should I do? Education in my home country is very expensive and getting scholarship for postgraduate studies is not possible because I have a poor BSc (low GPA, no papers, etc). So I decided to study my Master degree in a country with much cheaper tuition fees, so that I can make up for my academic record and getting an admission for PhD with scholarship in my home country. Unfortunately 'the custom' in the new country is like that the professors (would-be supervisors) are those who give the admission and they strongly prefer to take students who will stay for PhD as well. But I want to come back after finishing my Master degree especially for being with my family. 

To avoid consequences and also ethical reasons telling the truth that I won't continue to PhD is a must. A friend of mine suggested this website. I would highly appreciate for any advice for the most suitable ways of approaching and opening up the issue with the would-be supervisor?
I would highly appreciate for any advice for the most suitable ways of
  approaching and opening up the issue with the would-be supervisor?


When you apply for a PhD, you will need letters of reference. Among them, the one from the supervisor is the most important. If you lie to your supervisor, it may be extremely difficult to get a PhD wherever you apply.

If you don't plan to pursuing a PhD after your Master, tell the potential supervisor exactly that. If he doesn't agree, move on until you find the one that agrees.