You can see " http://www.italki.com/question/310282" .

Thanks = Arigatou ありがとう Thank you = Arigatou ありがとうございます Thank you very much = Makotoni arigatou gozaimasu　まことにありがとうございます 　　　　　　　　　　　　　　　　Hontouni arigatou gozaimasu ほんとうにありがとうございます 　　　　　　　　(very polite) Kokoroyori kansya moushiagemasu こころよりかんしゃもうしあげます

"Doomo Arigatoo Gozaimasu"

I see, and two members have already answered you. Please check them out. Good luck to your Japanese.

how to say "thank you very much " in Japanese