It seems that this ruling will make Japan’s libel laws for Internet postings similar to what we currently see in Korea:

The Supreme Court has ruled that individuals posting comments on the Internet must be held to the same standards for criminal libel as writers in other forms of media.

The unprecedented ruling means that individuals can be held criminally responsible for their Internet postings.

In its decision dated Monday, the court’s First Petty Bench rejected an appeal filed by a 38-year-old man found guilty by the Tokyo High Court of libel in connection with his postings about a company that operated franchise ramen shops.

Between October and November 2002, the man wrote on his own website that the company was a “cult group.”

He was indicted in 2004 for libel.

The Tokyo District Court found the man not guilty on grounds that individuals who make Internet postings should be held to a looser standard for libel than mass media companies and experts who place content on the Internet.

However, the Tokyo High Court overturned the lower court ruling and handed down a fine of 300,000 yen (about $3,300). The man appealed to the Supreme Court.  [Asahi]