Live together in Japan

Do you think Live together is permitted according to Japanese culture
My Japanese girlfriend want to stay with me in my house what I rented for myself.
or According to house rental Law.
or Can two person stay together without married.

I live here with my Japanese girlfriend. We are not married, people sometimes ask us about marriage, but nobody thinks it is strange. Of course it is permitted! This is Japan, not Qatar.

Check your rent agreement to see if they say anything about additional resident.

"but nobody thinks it is strange"
that is not true.
even when they think it is strange, they don't say it straightforwardly, because telling such things is not polite.
they may ignore you sometimes (or often).
they may not help you and your girlfriend, when you get some troubles in future.
such behaviors are quite ordinary.

I trust the judgement of my partner and her family over you, �gken�h for the internet. You are welcome to disagree, but you are wrong. Nobody thinks it is strange.

It is unacceptable here in Japan, even if no one points it out.

haha,
you can compare this situation to tattoo acceptance in Japan.
probably some Japanese say OK for tattoo, and I am sure that most of Japanese say NO.
of course, Japanese who have tattoo say OK, because NO means that they deny their life styles by themselves.

The only person you have to concern yourself with their acceptance is the person who leased you the apartment. If they say "no", then to him/her it's not appropriate and hence the denial of living/cohabitation agreement.

I believe this depends on the generation - my parents (80s) would never have allowed it, I (now in my 50s) grew up being under their influence, but I did it anyways during my 20s.

I do hear of younger people (20s - 30s) living together before getting married, or simply living together. So. If her parents are OK with it, that's that.