Goran2812 wrote:it's said it's nissan's high quality brand, just like toyota have lexus etc... so, american? i really don't think so...

I believe that Lexus was created for the US market because Toyota had a reputation for building low quality cars for the budget consumer : they felt that their brand was not synonymous with the qualities needed for a successful entry into the US luxury car market, so spun off a rebranded subsidiary that could stand on its own merit.
From the opening paragraph of the Infiniti wiki article, this is exactly the same strategy that Nissan took for breaking into the same market : Infiniti started selling in the US before any other country BUT is not sold in Japan, so I would think it reasonable to assume that Infiniti is a US registered corporate subsidiary (though I would need to do some more research to confirm that).
http://en.wikipedia.org/wiki/Infiniti
Infiniti (Japanese: インフィニティ, Infiniti?) is the premium or luxury division of Japanese automaker Nissan Motors. Infiniti officially started selling vehicles on November 8, 1989 in North America. Marketing operations have since grown to include the Middle East, South Korea, Russia, Taiwan, China, and Ukraine. Infiniti began sales in additional European markets in late 2008. The marketing network for Infiniti-branded vehicles now includes over 230 dealers in over 15 countries.
The marque is not used in Japan and the automaker markets most of equivalent Infiniti models domestically as Nissans: Infiniti G as the Nissan Skyline sedan and coupe, Infiniti M as the Nissan Fuga, Infiniti EX as the Nissan Skyline crossover, and Infiniti Q45 as the Nissan Cima. The Infiniti FX has no Nissan equivalent and is not sold in Japan.
On a personal note, I
HATE the branding : every time I type Infiniti, my fingers reach for the Y key and I have to force myself to type that 4th I (shuddering as I do so) ...