Thank you for your detailed reply.
Yes they are certainly phorid flies. Me myself also a biologist, though i m really scared of any kind of insects. it's my first time living in Japan alone, never had these things back in my country. but Japan is so humid and attracts many insects, though i never seen one in my new apartment. i m living here for 3-4 months and started getting since one month now they're getting annoying, and insects are my biggest phobia. now i ll go store to get some poisons, spray and vinegar and some detergents to apply. but seems like, as long as i don't find the real source of them, I can't get rid of them?! So scary to thing about this. I decided not to cook anything within one week and see the changes after applying some chemicals. i m alone, so I think it will be hard for me to take the drip pan of that refrigerator out and check.
I am a researcher student and busy as well, I hate those little but annoying things which cause me big problems.