Sorry I cannot type Chinese here

I will go to Japan for a business trip and will stay there for about 3 weeks. Can anybody tell me what files I need to apply for a Japan visa from US? I checked their website, found they need:

1. Passport; 2. Application form; 3. Invitation letter from Japan; 4. My airflight ticket; 5. Letter from my employer to show they will be responsible for my expense.

Anything else? Somebody said I will need a US visa to show them that I can come back to US, somebody said I don't need it. Which one is true?

Another important question, may I apply for my US visa from Japan? I need a new H-1 stamp.

Thank you. Thank you. Thank you.