What kind of documentation is required for a business visa for an Australian when applying in Japan

Our subsidiary in Shanghai checked with the Shanghai Municipal Commission of Commerce, and were told that an invitation letter from them should be ok for my application.
Previously I was told that this was insufficient to obtain a visa and needed some more formal government paperwork, can you please clarify what type of documentation is required. I will be visiting Shanghai for business (3 days) and some leisure (3 days).