The professor takes me only if I continue up to finishing PhD. What should I do?
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.