Recomendation letter Can a lecturer from another faculty write a reference letter for me for my masters degree.
This lecturer has introduced me to many parent to teach their student based on my field and the result has been so good and he us willing to write me a reference letter.
Can he?
Actually, anyone can write you a letter. The best letters are from those who can help a reader evaluate your suitability for a degree and your likelihood of success in it. Usually that is people closest to your studies, but others can also be helpful. 

Evaluate what you think each potential writer will say about you. It may actually be good if they say different, but positive, things. 

The only letters that might be discounted, I think, are those that might be judged to be biased in your favor for non academic reasons. A letter from one of your parents or siblings, for example.